Magnetic Nanomaterials: Synthesis, Characterization and Applications 9783031360879

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Magnetic Nanomaterials: Synthesis, Characterization and Applications

Table of contents :
Engineering Materials Series
Magnetic Nanomaterials: Synthesis, Characterization and Applications
About the Editors
An Overview of Magnetic Nanomaterials
1. Introduction
2. Synthesis and Characterization of MNMs
2.1 Synthesis Techniques of MNMs
2.2 Characterization Techniques of MNMs
3. Applications in of MNMS
3.1 Biomedical Applications of MNMs
3.2 Agricultural Applications of MNMs
3.3 Environmental Applications of MNMs
3.4 Catalytic Applications of MNMs
4. Conclusion and Outlook of MNMs
Magnetic Nanomaterials: Synthesis and Characterization
1. Introduction
2. Type of Magnetic Nanomaterials
2.1 Metallic Magnetic Oxides
2.2 Metal Alloy Magnetic Nanostructures
2.3 Graphene Oxide/Metal Nanocomposites
3. Method of Synthesis
3.1 Sol–Gel Method
3.2 Thermal Decomposition
3.3 Hydrothermal Method
3.4 Other Methods
4. Characterization of Magnetic Nanomaterials
4.1 X-ray Diffraction
4.2 Scanning and Transmission Electron Microscopy
4.3 Raman Spectroscopy
4.4 Thermal Stability Properties
4.5 X-ray Photoelectron Spectroscopy
4.6 Ultraviolet Photoelectron Spectroscopy
4.7 X-ray Absorption Near Edge Structure Spectroscopy
4.8 Magnetic Hysteresis Loop Measurements
5. Conclusion
Utility of Magnetic Nanomaterials for Theranostic Nanomedicine
1. Introduction
2. Routes for Iron Oxide Magnetic NPs (IOMNPs) Synthesis
2.1 Thermal Decomposition Technique
2.2 Microemulsion Technique
2.3 Hydrothermal Technique
2.4 Precipitation Technique
2.5 Sonochemical Technique
3. TRC Utilization of MNPs
3.1 MHT
3.2 MRI
4. Optical Intrusion Techniques Employing MNPs for Cancer Treatment
4.1 PTT
4.2 PDT
5. Conclusion
Magnetic Nanomaterials for Heavy Metals Detection
1. Introduction
2. HMs
3. HMs Detection
3.1 Sensors for Sensing HMs
4. Conclusion
Magnetic Nanomaterials for Dye Sensing and Removal
1. Introduction
2. Types of MNPs and Their Properties
2.1 Types of MNPs
2.2 Properties of Magnetic Nanomaterials
3. Sensing Principles of MNPs
4. Applications of MNPs in Dye Sensing
5. Studies on the Use of MNPs for Dye Sensing
6. Conclusions and Future Prospects
Magnetic Nanomaterials Applications in Solar Cells
1. Introduction
2. Brief Review on Magnetism
2.1 Types of Magnetism
2.2 Important Quantities in Magnetism
3. Thermal Properties of Magnetic Materials
4. Nanomaterials
4.1 Magnetic Nanomaterials
4.2 Properties of Magnetic Nanomaterials
5. Solar Cells
6. Advantages/Applications of Magnetic Nanomaterials in Solar Cells
7. Conclusion
Applications of Magnetic Nanomaterials for Wastewater Treatment
1. Introduction
2. MNMs Fabrication
3. Application of MNMs for HMs and Dyes Sequestration
3.1 IO-Based NMs for HMs and Dyes Removal
3.2 Ce-Oxide Based NMs for HMs and Dyes Elimination
3.3 Ti-Oxides Based NMs for HMs and Dyes Elimination
3.4 Al-Oxides-Based NMs for HMs and Dyes Elimination
3.5 Mn-Oxides Based NMs for HMs and Dyes Elimination
4. Effects of Various Factors on the HMs and Dyes Sorption to MNMs
4.1 Impact of pH
4.2 Influence of Sorbent Dose
4.3 Influence of Contact Time
4.4 Influence of Initial Sorbate Concentration
5. Isotherms and Kinetic Models for the SP of HMs and Dyes to Various MNMs
6. Thermodynamics
7. Conclusions and Future Prospective
Magnetic Nanomaterials for Decontamination of Soil
1. Introduction
2. Magnetic FeO NPs (MFeONPs) Synthesis
2.1 Biological Synthesis
2.2 Zero-Valent Iron NPs (ZVI-NPs)
2.3 FeO(s)
2.4 Fe3O4
2.5 c-Fe2O3
2.6 Spinel Ferrites and Their Composites
3. The Fate of NPs in Soil
4. Decontamination of Soils Using NPs
4.1 PAH Remediation Using Activated Carbon-Based Nanomaterial
4.2 MNPs
5. Environmental Effect of Magnetic NMs in Soil Remediation
6. Conclusions
Magnetic Nanomaterials-Based Sensors for the Detection and Monitoring of Toxic Gases
1. Introduction
2. Magnetic Nanomaterials-Based Sensors
3. Electrochemical Sensing Devices
3.1 Principle of Electrochemical Sensor
4. Optical Sensing Devices
4.1 Optical Sensing Applications
5. Piezoelectric Sensors
5.1 Working of Piezoelectric Sensor
6. Magnetic Field Sensing Devices
7. Conclusion
Application of Magnetic Nanomaterials as Drug and Gene Delivery Agent
1. Introduction
2. Conjugation of Magnetic Nanomaterials
3. Stimuli-Responsive Control of Drug Release and Translation Into Clinics
3.1 Magnetic Nanomaterials in MRI-Assisted Drug Delivery
3.2 Magnetically-Engineered Drug Delivery
3.3 Vectorized Nano-vehicles Drug Delivery
3.4 Stimuli-Responsive Drug Delivery
4. Conclusion and Future Projections
Role of Magnetic Nanomaterials in Biosafety and Bioregulation Facets
1. Introduction
2. Biomedical Applications of NPs Vis-À-Vis MNPs
2.1 Nanomedicine
2.2 Drug Carriers
2.3 Medical Instruments
2.4 Tissue Engineering
2.5 Therapeutic Drugs
2.6 Nanogene Medicine
2.7 GT of Cancer
2.8 Nanovaccines
2.9 Radiosensitizers in Radiation Therapy
3. HBS of MNPs Used in Clinical Trials
4. MNPs’ HBS and Hazard Issues
5. Conclusions and Suggestions for Research Strategies
Potentialities of Magnetic Nanomaterials in Tissue Engineering Applications
1. Introduction
1.1 Some Terminology Frequently Adopted in MNM Studies
2. Pillars of Tissue Engineering
3. Nanomaterials
3.1 Hydrogels
3.2 Nanospheres (NS)
3.3 Metals Polymer
3.4 Ceramics and Glass–Ceramics Polymer
3.5 Natural and Synthetic Polymers
4. Types of MNM for Tissue Engineering
4.1 Bond Structure of MNM
5. Methods of MNM Synthesis
6. Methods of MNM Characterisation
7. Application in Body Tissue Systems
8. Hydrogels in Tissue Engineering
9. Applications of MNM in Tissue Engineering
9.1 Applications of MNM in Lung Engineering
9.2 Applications of MNM in Skin Engineering
9.3 Applications of MNM in Bone Engineering
9.4 Applications of MNM in Liver Engineering
9.5 Applications of MNM in Pain Management
10. Perimeters of Applications
10.1 Magnetisation Changes Within Particles
10.2 Inspection of Tissue or Organs Using MNM Technology
10.3 Conclusion
Utilization of Magnetic Nanomaterials for Combating Pathogens
1. Introduction
2. Mechanisms of Magnetic Nanomaterials (NMPs) on Pathogens
3. Therapeutic Potentials of Magnetic Nanomaterials Against Yeast, Bacteria, Fungi, and Bacteria
4. Health and Environmental Impacts of Magnetic Nanomaterials
5. Conclusion and Recommendations

Citation preview

Engineering Materials

Uyiosa Osagie Aigbe Kingsley Eghonghon Ukhurebor Robert Birundu Onyancha Editors

Magnetic Nanomaterials Synthesis, Characterization and Applications

Engineering Materials

This series provides topical information on innovative, structural and functional materials and composites with applications in optical, electrical, mechanical, civil, aeronautical, medical, bio- and nano-engineering. The individual volumes are complete, comprehensive monographs covering the structure, properties, manufacturing process and applications of these materials. This multidisciplinary series is devoted to professionals, students and all those interested in the latest developments in the Materials Science field, that look for a carefully selected collection of high quality review articles on their respective field of expertise. Indexed at Compendex (2021) and Scopus (2022)

Uyiosa Osagie Aigbe · Kingsley Eghonghon Ukhurebor · Robert Birundu Onyancha Editors

Magnetic Nanomaterials Synthesis, Characterization and Applications

Editors Uyiosa Osagie Aigbe Department of Mathematics and Physics Cape Peninsula University of Technology Cape Town, South Africa

Kingsley Eghonghon Ukhurebor Department of Physics Edo State University Uzairue, Edo State, Nigeria

Robert Birundu Onyancha Department of Technical and Applied Physics Technical University of Kenya Nairobi, Kenya

ISSN 1612-1317 ISSN 1868-1212 (electronic) Engineering Materials ISBN 978-3-031-36087-9 ISBN 978-3-031-36088-6 (eBook) © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

To our families: past, present, and future.


First and foremost, we are most grateful to Almighty God, our creator, who kept us alive and gave us all we needed to make this book a success. We owe Him everything. We have always been and will forever be grateful to Him. Our profound gratitude goes to our respective institutions’ management, who have always been of great assistance in our research and academic developments. We are also grateful to all the chapter contributors as well as the authors and publishers whose publications were used as a basis for writing this book, without whom this book would not have been possible. We thank our families, mentors, colleagues, friends, and all who contributed and are still contributing in one way or another towards the success of our academic and research abilities as well as our other endeavours. May God bless you all richly!



An Overview of Magnetic Nanomaterials. . . . . . . . . . . . . . . . . . . . . . . . . . . . Kingsley Eghonghon Ukhurebor, Uyiosa Osagie Aigbe, Robert Birundu Onyancha, Vincent Aizebeoje Balogun, Osikemekha Anthony Anani, Kenneth Kennedy Adama, Kaushik Pal, Heri Septya Kusuma, and Handoko Darmokoesoemo


Magnetic Nanomaterials: Synthesis and Characterization. . . . . . . . . . . . . David O. Idisi, Chinedu C. Ahia, and Edson L. Meyer


Utility of Magnetic Nanomaterials for Theranostic Nanomedicine ...... Uyiosa Osagie Aigbe, Robert Birundu Onyancha, Kingsley Eghonghon Ukhurebor, Benedict Okundaye, Efosa Aigbe, Omamoke O. E. Enaroseha, Kingsley Obodo, Otolorin Adelaja Osibote, Ahmed El Nemr, Luyanda Lunga Noto, and Harrison I. Atagana


Magnetic Nanomaterials for Heavy Metals Detection. . . . . . . . . . . . . . . . . Ikenna Chibuzor Emeji, Chike George Okoye-Chine, Orlando Garcia-Rodriguez, Ephraim Igberase, and Peter Ogbemudia Osifo


Magnetic Nanomaterials for Dye Sensing and Removal ............... Joan Nyika and Megersa Olumana Dinka


Magnetic Nanomaterials Applications in Solar Cells . . . . . . . . . . . . . . . . . . 113 D. M. Jeroh, L. E. Esiekpe, J. C. Ejeka, and P. O. Isi Applications of Magnetic Nanomaterials for Wastewater Treatment . . . . 129 Uyiosa Osagie Aigbe, Kingsley Eghonghon Ukhurebor, Robert Birundu Onyancha, Benedict Okundaye, Efosa Aigbe, Heri Septya Kusuma, Luyanda Lunga Noto, Otolorin Adelaja Osibote, and Harrison I. Atagana




Magnetic Nanomaterials for Decontamination of Soil . . . . . . . . . . . . . . . . . 171 Onyedikachi Ubani, Sekomeng Johannes Modise, and Harrison Ifeanyichukwu Atagana Magnetic Nanomaterials-Based Sensors for the Detection and Monitoring of Toxic Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Joseph Onyeka Emegha, Timothy Imanobe Oliomogbe, and Adeoye Victor Babalola Application of Magnetic Nanomaterials as Drug and Gene Delivery Agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 Robert Birundu Onyancha, Bill C. Oyomo, Uyiosa Osagie Aigbe, and Kingsley Eghonghon Ukhurebor Role of Magnetic Nanomaterials in Biosafety and Bioregulation Facets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 Heri Septya Kusuma, Kingsley Eghonghon Ukhurebor, Uyiosa Osagie Aigbe, Robert Birundu Onyancha, Ikenna Benedict Onyeachu, and Handoko Darmokoesoemo Potentialities of Magnetic Nanomaterials in Tissue Engineering Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 Benedict Okundaye, Uyiosa Osagie Aigbe, and Kingsley Eghonghon Ukhurebor Utilization of Magnetic Nanomaterials for Combating Pathogens . . . . . . 253 Osikemekha Anthony Anani, Kenneth Kennedy Adama, Kingsley Eghonghon Ukhurebor, Habib Aishatu Idris, Vincent Kenechi Abanihi, and Vincent Aizebeoje Balogun

About the Editors

Uyiosa Osagie Aigbeis a research fellow with the Department of Mathematics and Physics, Faculty of Applied Science, Cape Peninsula University of Technology, Cape Town, South Africa. He obtained his Ph.D. degree in Physics from the prestigious University of South Africa, Pretoria, South Africa. He is currently a member of several learned academic organizations. His research interests are in applied physics, nanotechnology, fluid dynamics, water purification processes, image processing, environmental physics, and material science. He has also served as a reviewer for numerous highly regarded journals. He has authored and co-authored several research publications. Kingsley Eghonghon Ukhurebor is a lecturer/ researcher and the present acting head of the Department of Physics at Edo State University, Uzairue, Nigeria, and a research fellow at the West African Science Service Center on Climate Change and Adapted Land Use (WASCAL), Competence Center, Ouagadougou, Burkina Faso, a Climate Institute sponsored by the Federal Ministry of Education and Research, Germany. He had a Ph.D. in Physics Electronics from the University of Benin, Benin City, Nigeria. He is a member of several learned academic organizations, such as the Nigerian Young Academy (NYA), etc. His research interests are in applied physics, climate physics, environmental physics, telecommunication physics, and material science (nanotechnology). He serves as editor and reviewer for several reputable journals and publishers, such as Springer Nature, Elsevier, the Royal Society xi


About the Editors

of Chemistry (RSC), the Institute of Physics (IOP), Taylor & Francis, John Wiley & Sons, the IEEE, Frontiers, Hindawi, etc. He has authored or co-authored several publications with these reputable journals and publishers. He is presently ranked among the top 50 authors in Nigeria by Scopus scholarly output. Robert Birundu Onyanchais a lecturer and researcher working fulltime at the department of Technical and Applied Physics, School of Physics and Earth Science at the Technical University of Kenya. He holds a Ph.D. in Physics from the University of South Africa. His research interests are in material science, waste water treatment technologies, superconductivity and magnetism. He is a registered member of various research bodies and has authored and co-authored research papers and book chapters which have been published in reputable and accredited in journals and publishers. Furthermore, he serves as an editor and reviewer of highly accredited and trustworthy journals.

An Overview of Magnetic Nanomaterials Kingsley Eghonghon Ukhurebor, Uyiosa Osagie Aigbe, Robert Birundu Onyancha, Vincent Aizebeoje Balogun, Osikemekha Anthony Anani, Kenneth Kennedy Adama, Kaushik Pal, Heri Septya Kusuma, and Handoko Darmokoesoemo

Abstract Like every other nanomaterial (NM) or nanoparticles (NPs), magnetic nanomaterials (MNMs) or magnetic nanoparticles (MNPs), utilize bionanomaterials (BNMs), nanosized materials composed of various biological entities. MNMs are advanced materials that, once synthesized and characterized, can be used in solar cells, theragnostic nanomedicine, drug and gene delivery agents, tissue engineering, K. E. Ukhurebor (B) Department of Physics, Faculty of Science, Edo State University, Uzairue, Edo State, Nigeria e-mail: [email protected]; [email protected] U. O. Aigbe Department of Mathematics and Physics, Faculty of Applied Sciences, Cape Peninsula University of Technology, Cape Town, South Africa R. B. Onyancha Department of Technical and Applied Physics, School of Physical Sciences and Technology, Technical University of Kenya, Nairobi, Kenya V. A. Balogun Department of Mechanical Engineering, Edo State University, Uzairue, Edo State, Nigeria O. A. Anani Laboratory for Ecotoxicology and Forensic Biology, Department of Biological Science, Faculty of Science, Edo State University, Uzairue, Edo State, Nigeria K. K. Adama Department of Chemical Engineering, Faculty of Engineering, Edo State University, Uzairue, Edo State, Nigeria K. Pal University Centre for Research and Development (UCRD), Department of Physics, Chandigarh University, Gharuan, Mohali, Punjab, India Laboratório de Nànóteknólógià, University Federal Rio de Janeiro, Rio de Janeiro, Brazil H. S. Kusuma Department of Chemical Engineering, Faculty of Industrial Technology, Universitas Pembangunan Nasional “Veteran” Yogyakarta, Yogyakarta, Indonesia H. Darmokoesoemo Department of Chemistry, Faculty of Science and Technology, Airlangga University, Surabaya, Mulyorejo, Indonesia © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 U. O. Aigbe et al. (eds.), Magnetic Nanomaterials, Engineering Materials,



K. E. Ukhurebor et al.

biosafety and bioregulation aspects, pathogen combat, wastewater treatment, soil decontamination, detection, sensing, and monitoring of heavy metals, dyes, toxic gases, and so on. Several MNMs or MNPs have been utilized for applications in biomedical, agriculture, and environmental (atmospheric, aquatic, and terrestrial) fields. Hence, this introductory chapter presents a summarized highlight of the various synthesis and characterization techniques of MNMs, along with the various applications and potentialities of MNMs both in the biomedical, agricultural, and environmental fields, as well as catalytic processes which is the major aim of this book. Also, some outstanding prospects of MNMs or MNPs in biomedical, agricultural, and environmental applications are highlighted in the conclusion section. Keywords Agriculture · Biomedical · Environment · Nanomaterials · Nanotechnology · Magnetic nanomaterials

1 Introduction Exciting scientific and technological advancement is one of the utmost gains to humanity [1, 2]. Its potentiality to manoeuvre innovative materials of various dimensions has generated an evolution in the scientific and technological fields that has improved the lives of human beings, and nanotechnology (NTech) remains one of the major contributors to this evolution [3, 4]. Contemporary advances in the field of NTech have helped to advance and revolutionize a variety of industries. The number of advantages and uses for NTech is expanding quickly and have advanced scientific and technological field, and it has been considered one of the best technologies for studying the properties, synthesis, characterization, and applications of nanosized constituents [3]. They differ from their parent bulky materials in that they are small particles with an average dimension range of between 1.00 and 100.00 nm, which makes them suitable for a variety of applications [3, 5]. Among these, magnetic nanoparticles (MNPs) or magnetic nanomaterials (MNMs), a nanoscale substance with exceptional magnetic features, have found extensive use in a variety of industries, including biomedical, engineering, energy, and environmental applications. Due to their distinct and distinctive features, which could make them valuable in biomedical, agriculture, environmental (atmospheric, aquatic, and terrestrial) fields and catalysis processes [6]. MNMs have recently become the focus of intense investigation [6]. Hence, Researchers’ interest in the possibility of increasing a material’s potential at the nanoscale has led to success on a worldwide scale in practically all fields [7]. Due to the potential, they present, MNMs or MNPs are a type of materials that have drawn interest from the research community. Their capacity to alter their morphology and particle size has resulted in the modification of their spin alignment [8]. For a variety of uses, the tuning of the spin alignment can be gathered. For soft magnet applications, for instance, the saturation magnetism seen in ferromagnetic nanomaterials (NMs) or nanoparticles (NPs) is essential because it makes scaling up

An Overview of Magnetic Nanomaterials


and shrinking simple [6]. Modern industries have undergone significant change as a result of numerous NM applications [3]. MNMs or MNPs have engrossed study attention lately owing to their environmental, agricultural, biomedical and industrial applications [6, 9]. Evidently, several MNMs have been utilized for applications in biomedical, agriculture, and environmental (atmospheric, aquatic, and terrestrial) fields, and these synthesized and characterized MNMs are used in solar cells, theragnostic nanomedicine, drug and gene delivery agents, tissue engineering, biosafety and bioregulation aspects, pathogen combat, wastewater treatment, soil decontamination, detection, sensing, and monitoring of heavy metals (HMs), dyes, toxic gases, etc. Hence, this chapter, which is an overview of MNMs and is the introductory part of this book titled “MNMs-synthesis, characterization, and applications”, will briefly highlight the various synthesis and characterization techniques of MNMs, along with an overview on MNM’s basic applications/utility in biomedical, agriculture, and environmental (atmospheric, aquatic, and terrestrial), as well as catalytic processes along with the prospects and topical tendencies. A diagrammatic illustration of this introductory chapter is shown in Figs. 1 and 2 illustrates the various chapters contained in this book. Additionally, this book attempts to emphasize the synthesis and characterization of MNMs in Chap. 2. Chapter 3 deals with the utility of MNMs for theragnostic nanomedicine, while Chap. 4 is on MNMs for HMs detection, and Chap. 5 discusses MNMs for dye sensing. MNMs’ applications in solar cells are discussed in Chap. 6 and the applications of MNMs for wastewater treatment are discussed in Chap. 7.

Fig. 1 A diagrammatic illustration of this introductory chapter (MNMs: magnetic nanomaterials)


K. E. Ukhurebor et al.

Fig. 2 An illustration of the various chapters contained in this book (MNMs: magnetic nanomaterials)

Chapter 8 covers MNMs for soil decontamination, and Chap. 9 is on MNMs-based sensors for the detection and monitoring of toxic gases. Chapter 10 will deal with the application of MNMs as drug and gene delivery agents, followed by Chap. 11, which deals with the role of MNMs in biosafety and bioregulation facets. The potentialities of MNMs in tissue engineering applications are discussed in Chap. 12, while Chap. 13, which is the last chapter of this book, will deal with the utilization of MNMs for combating pathogens.

2 Synthesis and Characterization of MNMs This section briefly highlights the various synthesis techniques and characterization techniques of MNMs.


Synthesis Techniques of MNMs

The development of various methods for the synthesis of MNMs or MNPs has been the focus of intense research during the last few years. Several synthetic techniques

An Overview of Magnetic Nanomaterials


Fig. 3 Pictorial diagram of the synthesis of MNMs or MNPs prepared through various biological, chemical, and physical techniques. Adapted from Ali et al. [9]; Copyright, Frontiers publishers, 2019. Reprinted with permission from Frontiers publishers from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY). (MNPs: magnetic nanoparticles, NPs: nanoparticles)

are utilized to produce MNMs with the necessary size (dimension), shape, stability, and biocompatibility. The most popular techniques for synthesizing MNMs are; “ball milling, thermal decomposition, coprecipitation, sol–gel, hydrothermal, microemulsion, and biological techniques”. Figure 3 contains a schematic/pictorial illustration/ diagram of the synthesis of MNMs prepared through various biological, chemical, and physical techniques as adopted by Ali et al. [9].


Physical Techniques

The physical techniques use both top-down and bottom-up strategies. Through high intensity ball milling, the bulk constituents are reduced to nanoparticle size in the top-down method. It is challenging to produce NPs through mechanical crushing that are the required form and size [10]. In contrast to the top-down strategy, the bottomup method can produce fine, well-dispersed nanoparticles. A bottom-up strategy example is laser evaporation [11]. MNPs are also created using different physical


K. E. Ukhurebor et al.

techniques such as the wire explosion technique and the inert-gas condensation technique. Some of the commonly used physical techniques are mechanical/ball milling technique [12], wire explosion technique [13, 14], and laser evaporation technique [11].


Chemical Techniques

The various bottom-up processes used in chemical synthesis are diverse. In a recent review publication by Ali et al. [9], several popular techniques that are frequently employed in synthesizing MNMs are comprehensively described. These commonly used chemical techniques are coprecipitation technique [15–18], thermal decomposition technique [19–22], microemulsion synthesis technique [18, 23, 24], hydrothermal synthesis technique [24–27], and sol–gel technique [12, 28, 29].


Biological Techniques

Biological synthesis is one of the well-known techniques for synthesizing MNMs [9], which involves employing living things like plants and microorganisms (such as actinomycetes, fungi, bacteria, and viruses) [30]. This approach creates MNMs that are comparably biocompatible and have practical uses in the biomedical industry. This approach has advantages in terms of effectiveness, environmental friendliness, and clean procedure. The drawback is the NMs’ ineffective dispersion [31]. Researchers are now very interested in the production of NMs employing the tissues, extracts, exudates, and other components of plants [32]. For instance, ferromagnetic magnetite particles with an average size of 60 nm have reportedly been produced naturally [33]. The use of microorganisms and plants (biological) to produce NMs is one of the potential methods that have just come to light for the synthesis of MNMs, although the mechanism by which this occurs is still poorly understood [31, 34]. For instance, some research offered potential processes for metal NM mycosynthesis [9]. Nitrate reductase activity, shuttle electron quinones, and a mixed process are the three proposed mechanisms [9]. However, the process of acknowledging MNM preparation is not particularly clear [31]. The Suzuki–Miyaura reaction and photocatalysis were both carried out using biologically produced Fe3 O4 magnetic material as a catalyst [27]. This approach has some drawbacks that need more research, such as yield and MNM dispersion [34, 35]. However, utilizing magnetism to help separate biosorbents from the solution and increase efficiency is a relatively recent development that is now clearly attracting attention. This entails using external magnetic fields and employing magnetic biosorbents during the biosorption process [6, 36].

An Overview of Magnetic Nanomaterials



Characterization Techniques of MNMs

To evaluate the physicochemical characteristics of MNMs, they are characterized using a variety of equipment [37–43]. The display of many physicochemical features of NMs depends significantly on their size. Their characteristics can be altered by even a slight change in their nanoscale dimension [9]. The following are some of the most commonly used tools for the characterization of MNMs: “Atomic Force Microscopy (AFM), Energy Dispersive X-ray Diffraction (EDXD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FT-IR) Spectroscopy, UV Spectrophotometer, Transmission Electron Microscopy (TEM), and Mossbauer Spectroscopy (MS) are a few of the tools used for the characterization of MNMs” [9, 44].

3 Applications in of MNMS The MNMs have attracted lots of consideration in the last few years owing to their promising outcomes in a variety of sectors [9]. MNMs’ applicability is made more promising by their super/exceptional-magnetic characteristics, distinctive dimensions and form, high surface area and volume ratio, and biocompatibility [6]. These characteristics have drawn researchers from various fields to it [9]. In this section of this introductory chapter, we have briefly discussed the endowed applications of MNMs in a number of well-known fields, such as the biomedical, agricultural, and environmental domains, as well as catalytic processes.


Biomedical Applications of MNMs

As a result of their numerous physicochemical characteristics, simplicity in synthesis, biocompatibility, and stability, MNMs have recently been widely used in numerous biological applications [1, 9, 45]. External magnetic fields can affect MNMs. Magnetic resonance imaging can be improved by MNMs since they can change the magnetic fields nearby (MRI) [9, 46]. The translation, rotation, and energy dissipation that the externally applied magnetic field causes and creates in dipoles occur from several types of force and torque. Numerous applications of these phenomena exist, such as cell separation and biomarker transfer, magnetic drug administration, magneto-mechanical activation of cell surface receptors, biomedical imaging, bacterial theragnostic, drug release triggering, and hyperthermia. Depending on their use in various applications, several materials with different physical and magnetic properties make up the formulation of MNMs. However, in biomedical research, their potential biocompatibility or toxicity must be taken into account as the most


K. E. Ukhurebor et al.

crucial element [9, 47]. The following are some of the recognized biomedical applications of MNMs: cancer theranostics [48, 49], bacterial theranostics [25, 50–56], and biosensing [57, 58].


Agricultural Applications of MNMs

Numerous studies have been completed that demonstrate how well metallic nanoparticles can be used for soil quality improvement, plant protection, and seed germination effective application of metallic NMs in plant safety, seed germination, and enhancing soil quality [59, 60]. Iron (Fe) oxide MNMs, for instance, can be utilized as nutrients of the soil to boost production with the fewest adverse effects [61]. Fe is a very important element that is involved in many physiological processes, including respiration, biosynthesis, the production of chlorophyll, and redox reactions [62]. A number of plants, including peanuts, lack Fe. Numerous studies have been done in this field to use Fe NMs to treat the deficit and increase Fe consumption [63–66]. The majority of the time, NMs are used as nano-fertilizers in hydroponic systems rather than in the field. Fe is thought to be the soil nutrient that is most prevalent for plants. Its accessibility is still a problem for plants. Therefore, using analytical methods, functionalized Fe oxide NMs can circumvent this issue and overcome obstacles and uptake by plants [9]. Ju et al. [67], created water-soluble Fe oxide NMs (IONP-EDTA) by synthesising Fe oxide NMs through thermal decomposition and oleic acid capation (IONPOA), followed by a ligand exchange method with N-(trimethoxysilylpropyl) EDTA to track Fe absorption and transport in plants. They developed a technique to use magnetic particle spectroscopy to track the absorption and distribution of various chelating Fe NMs (10 and 20 nm). The authors demonstrate that there were more Fe ions produced by the larger IONP20-EDTA NMs than the smaller IONP10-EDTA. Regarding IONP20-EDTA treatment, there is a rise in the production of biomass and chlorophyll. Neither the size nor the shape of the constituent parts produced from the IONP10-EDTA or IONP20-EDTA samples exhibit any appreciable changes in the TEM images. The location of the Fe oxide NM build-up, which demonstrates the plant’s uptake route through roots. The dual paths for the uptake and translocation of the Fe oxide NMs into the upper components of the plants are also shown, along with the uptake of Fe via the root via various oxidation states (apoplastic and symplastic pathways). The use of MNMs in disease management is still evolving, despite the fact that many MNMs have been employed as antimicrobial agents in biomedical studies to treat innumerable types of plant diseases [68, 69]. For targeted delivery to certain sections of the plant, MNMs can be useful. Tracking the internal MNM movement is particularly useful for the focused treatment of particular plant areas [70]. It has been claimed that MNMs can be used for the transmission of biomolecules (BMs) into plant cells and that their magnetic properties can be used to direct conveyance and localization.

An Overview of Magnetic Nanomaterials


For instance, a study described treating plant diseases with carbon-coated magnetic Fe NMs and in vitro culturing of Cucurbita pepo. Using confocal, optical, and electron microscopy, the localisation was detected [71]. In intelligent delivery systems, the conjugation of MNMs with other BMs like nucleic acids, drugs, and enzymes is highly helpful. It is very effectively used to transfer a gene and have it expressed in the host cell. At present, three different categories of carrier systems— viruses, electroporation using nucleic acid, and transfection—are used to convey genes. For many medical issues, the transfection approach holds a very significant solution. Kudr et al. [21], use MNMs to coat cultivated cells to increase their transfection efficiency. The usage of NMs can increase cell toxicity, which limits their utility in certain in vivo and in vitro research studies.


Environmental Applications of MNMs

As a result of the increased release of hazardous and deadly chemicals and composites because of the anthropogenic activities, the degradation and contamination of the water (aquatic environment), soil (terrestrial environmental), and the air (atmospheric environment) are emerging as major environmental issues [72, 73]. Pharmaceuticals, pesticides, industrial wastes, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons are only a few examples of the numerous organic pollutants that are permanently present in the environment [9, 74–76]. Groundwater, ocean, sewage effluents, and drinking water all include various types of organic contaminants. When such types of persistent organic contaminants enter the food chain, humans may experience major health issues [77, 78]. It’s crucial to plan and create efficient technologies in order to improve water quality. NTech has recently become one of the most advantageous and dependable alternatives to the conventional treatments’ techniques. For the treatment of water and air, metal oxides, carbon, and NMs have been reported. Direct injection of Fe NMs under pressure into the subsoil has shown to decompose the chlorinated composite (trichloroethylene), into environmentally benign composites. Similarly, this technique has been used to treat the immobilization of radionuclides and HMs [79–81]. It’s interesting to note that using MNMs to remove organic species, target bacteria, and degrade dye has been found to purify water. Fe3 O4 @amino acid for the magnetic separation of pollutants from effluent (wastewater) is one of the greatest examples. Three distinct amino acids, including arginine, lysine, and Poly-L-lysine, were added to the surface of Fe3 O4 NMs to modify and functionalize them, creating Fe3 O4 @Arinine, Fe3 O4 @Lysine, and Fe3 O4 @Poly-L-lysine. Both gram-positive and gram-negative bacteria, such as Escherichia coli and Bacillus subtilis, were better captured by the functionalized Fe3 O4 @AA. All three types of Fe3 O4 @AA were used to collect and eliminate approximately 97% of the germs [77]. Fe oxide’s magnetic feature makes it an efficient and simple separation method from aqueous solutions owing to the fact that they aggregate quickly when exposed to an external magnetic field [82].


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At present, magneto-catalysis is thought to be the most efficient approach for destroying persistent contaminants or dyes when used in stimulus–response systems. The underlying process is the catalytic breakdown of organic pollutants by magnetoelectricity (ME), which produces free radicals that combine with parent molecules to transform them into low-risk compounds [9]. Rhodamine B (RhB) and an alternating magnetic field have been used to test the MNMs’ ability to breakdown organic contaminants. For instance, Pane’s team designed “cobalt ferrite-bismuth ferrite (CFO-BFO) core–shell NMs” having ME properties to catalytically breakdown RhB, a model organic contaminant, and other pharmaceutical composites [83]. Without the use of catalytic chemicals, they created a ME system that uses a mixture of magnetostrictive CFO and multiferroic BFO to cleanse water by means of oxidation reactions under wireless or radio magnetic fields. The multiferroic shell BiFO3 (BFO) was made using the sol–gel technique, while the magnetostrictive CoFe2 O4 (CFO) NMs were made using a hydrothermal approach. Their research shows that as- synthesized NMs by ME induction produce hydroxyl and superoxide radicals, which catalytically breakdown (degrade) RhB with removal efficiency (RE) of 97.00% RE and a combination of pharmaceutical micropollutants with RE of 85.00% (see Fig. 4 as adapted from Mushtaq et al. [83]; Copyright, John Wiley & Sons, Inc. 2019). An important issue is the environment’s microbial pollution. Agricultural and industrial waste releases harmful ions and a wide variety of microbes into water bodies [72, 73, 84, 85]. The MNMs are used to kill and separate microbes, degrade dyes, and purify wastewater by removing organic and inorganic contaminants [6, 9]. Prior research has shown that MNNs with catalytic and photocatalytic properties can breakdown chemical pollutants such as pesticides and antibiotics through oxidation and reduction reactions [86]. Because of their stability, reduced aggregation, and significant surface area with reusing or recycling potential, MNM surfaces can be functionalized with stabilizers [87, 88]. Superparamagnetic Fe oxide NPs (SPIONPs) and their NPs have been used to remove organic contaminants [89]. NPs have been used to remove a variety of micropollutants [84], including harmful dyes [84, 90–92], and HMs [3, 84, 93]. According to a study, aminefunctionalized magnetite Fe3 O4 -SiO2 -NH2 NMs have been created to remove germs and viruses from water. These brand-new MNM types feature well-proven architectures and strong magnetic characteristics in both the core and shell. Pathogens of all kinds, including bacteriophages, the poliovirus-1, and bacteria like P. aeruginosa, Salmonella, and B. subtilis, are very drawn to the amine group in MNMs [94]. The transport and availability of Fe NMs in the atmosphere are poorly understood [9]. Because they are colloidal, pure Fe NMs have a limited ability to be transported and moved. According to reports, the migration of Fe NMs at the injection point is only a few feet [95]. Additionally, the speed/movement of NMs depends on the size, speed, pH, ion strength, the soil or groundwater composition, etc. [9, 96]. It should be highlighted that the most important factors, like toxicity and bioaccumulation, need to be considered. To assure the biosafety and stability of NMs, it is crucial to look at the toxicity mechanism [96]. To address the issues of water and

An Overview of Magnetic Nanomaterials


Fig. 4 A An outline of the magnetoelectricity effect induced catalytic breakdown (degradation) of organic pollutants employing core–shell CFO–BFO NPs under magnetic fields. B The catalytic breakdown (degradation) curves gotten for the model organic dye, RhB, under 15 mT and 1 kHz magnetic fields (n = 5). C The RE of a cocktail of five common pharmaceuticals employing the core–shell NPs (n = 4). (BFO: bismuth ferrite, CFO: cobalt ferrite, ME: magnetoelectric/ magnetoelectricity, NPs: nanoparticles)

soil quality, these research gaps must be fully filled. Compared to traditional techniques, wastewater treatment with nanotechnology has a huge potential to improve environmental quality. These techniques for water purification can decrease the need for chemicals, energy, and residual wastes. Consequently, using MNMs might significantly reduce the dangers connected to water cleaning procedures. With previously unheard-of opportunities to improve water and environmental quality, NTech has immense potential [97].


Catalytic Applications of MNMs

Different catalytic systems and procedures have been developed up to this point for the transformation of reactants into products [98]. The difficulty in separating homogenous catalysts from the reactions is one of their drawbacks. Utilizing catalysts assisted by MNMs, the heterogeneous catalysis constraint has recently been mitigated


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and eliminated [9]. When such catalysts are separated, the benefits of great dispersion and reactivity are combined with the ability of the MNMs to give a high surface area to assist active sites for reactants to be easily transformed into products [99]. Magnetic constituents with good repeatability in heterogeneous catalytic processes have been described [100–102]. The photocatalytic system has recently come into prominence as an effective and dependable technique for pollutant degradation in the presence of daylight. Sunlight is used in this system as an exterior stimulus source to turn on the system and produce free radicals, which then interact with contaminants to cause deterioration [9]. To this end, Xing’s team created “light-responsive magnetic hierarchical porous cadmium (Cd2+ ) imprinted photocatalytic nanoreactors (MHP-Cd)”, which have an outstanding capacity for adsorption for the breakdown of tetracycline [103]. Their research shows that by storing Cu2+ , Fe3+ , and Zn2+ outside the cavities, the homogeneous dispersion of MHP-Cd in Cd+2 solution enabled selective adsorption of Cd+2 there. The Cds absorbed the light after being added to the tetracycline solution with MHP-Cd and then exposed to sunshine, where they excited free electrons (e− ) and heat energy (h+ ). The transition of Fe3 O4 is aided by the creation of one e in the Cds. O2 used another e− to produce hydroxyl (OH) and superoxide (O2 ) radicals. A large quantity of tetracycline entered the mesoporous channels at the Cds surface due to the drug’s high affinity and was converted into carbon dioxide (CO2 ), water (H2 O), and smaller molecules (as shown in Fig. 5 as adapted from Lu et al. [103]). Additionally, it is necessary to create and implement appropriate strategies to regulate and finetune the particle size and form using various synthetic techniques. Designing and establishing extremely stable and reliable MNMs for industrial applications is still common practice. For such NMs to impede the reaction settings in heterogeneous processes, they must be sufficiently scalable and affordable [104].

4 Conclusion and Outlook of MNMs MNMs are a novel class of nanoscale materials composed of biological components such as antibodies, nucleic acids, proteins, etc. NTech’s advent has successfully sparked a scientific and technological evolution, and it has found use in a wide range of fields, including biomedical, agricultural, and environmental fields. MNMs are used in numerous industries, including biomedicine, the environment, agriculture, as well as catalytic processes. In this introductory part of this book, we have outlined recent developments in the synthesis, characterization, and prospective uses of MNMs. Different MNM types with potential features are being created utilizing various synthetic techniques. These techniques include; “sol–gel, ball milling, thermal decomposition, hydrothermal synthesis, microemulsion synthesis, thermal decomposition”, etc. Large-scale MNM synthesis is being done using physical techniques like ball milling. The milling jars and balls present a contamination risk with this technique. On the other hand, monodisperse MNMs are created via the thermal decomposition,

An Overview of Magnetic Nanomaterials


Fig. 5 A prototype photocatalytic and selective device of the MHP-Cd. As adapted from Lu et al. [103]; Copyright, ACS Publisher, 2019. Reprinted with permission from ACS Publisher

or pyrolysis, approach. The ease and superior control over MNM size of the pyrolysis process make it advantageous. At low processing temperatures, MNMs with uniform size distribution and enhanced stoichiometric control are created using the sol–gel synthesis technique. The approaches stated above suggest different MNM types for significant biological and biomedical applications. Numerous issues, such as cancer, pollution, agricultural practices, and others, have impeded human advancement. Different types of functionalized NMs have been created over the years to solve these issues. In order to treat cancer more effectively and safely, nanotechnologybased cancer therapy mostly relies on the effective and clever design of NMs. Due to their distinctive qualities, MNMs have recently contributed more to nanomedicines. Clinical research on various MNM modalities for cancer cell imaging and treatments has been conducted. Critical biological barriers that the synthesis and formulations of MNMs must overcome include localization at the target site, efficient drug administration to the cross-physiological communication, target site, and other methodological challenges unique to tumour. Clearance, endosomal escape, off-target locations, and drug efflux are some more types of obstacles. In both industrialized and developing nations, widespread bacterial resistance to antibiotics has emerged as a significant public health issue. The emergence and non-availability of new antibiotics will pose a severe concern because of the numerous types of multidrug-resistant bacteria. Strategies based on MNMs have been developed in the last ten years to effectively cure infections brought on by pathogenic bacteria and remove biofilms. MNMs play a significant function in targeted drug delivery and are often used. MNMs-based drug administration can lower drug doses compared to conventional drug delivery, which in turn lowers side effects.


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The MNMs also possess innate antibacterial action. They have synergistic therapeutic benefits when these antimicrobial compounds are combined with them, which increases the potency of antimicrobial medications. Similar to this, MNMs are used to purify wastewater, including the elimination of organic and inorganic contaminants, colour degradation, and the killing or isolation of bacteria. The MNPs can be used to control plant diseases and as soil fertilizers to boost yields. Research makes extensive use of the conjugation of MNMs with diverse BMs, including enzymes nucleic acids, and chemicals. In this way, a gene’s delivery and expression within the host cell are effectively utilized. In addition to other application disciplines, heterogeneous catalysis is one area where MNMs exhibit exceptional potential. In many forms of catalysis and clean energy, magnetic NMs have been employed to coat catalysts. For the conversion of the reactants into products, the MNMs can offer a large number of active sites. Designing and manufacturing MNMs for a variety of applications in many fields requires critical and productive research to overcome obstacles. Building regulatory structures for the safe and efficient use of nanotechnology must be taken into consideration as it advances and multidisciplinary approaches are made. In order to establish precise guidelines and platforms for advancing clinical trials and in vivo preclinical studies, there needs to be a regular method for communication between institutions and researchers. MNMs must overcome numerous obstacles before they can be used in the real world to cure cancer and stop drug resistance. It is necessary to discuss the proportion of MNMs to catalysts. The biocompatibility and long-term toxicity of the MNMs are two of the major difficulties. A highly thorough and in-depth investigation is required to examine the composition, morphology, size, form, structure, and side effects of MNMs. The research and synthesis/production of MNMs for a better future require the scientific community to handle such tremendous problems and conduct hassle-free clinical trials. The need for food is growing due to population growth and globalization, but there is a concomitant decline in the amount of agricultural land available. As a result, it is urgent to develop and modernize traditional agricultural practices. The agriculture sector is one of the largest sources of raw materials for the food and feed industries. The introduction of NTech has greatly expanded the agricultural industry as cuttingedge methods to boost crop output and nutrient content have been put into practice. In the realm of agriculture, NTech uses BNMs such as those formed from carbon, silica, etc. The development of chemical-free nano-fertilizers, nano-pesticides, and nano-insecticides frequently makes use of BNMs. Additionally, BNMs are employed in the creation of nano-biosensors (NBSs) for the detection of contaminants and nutrient concentrations in soil. The moisture content of the soil may now be accurately predicted by a novel wireless NBSs that uses BNMs. The safety and rules for creating nano-fertilizers are highly significant and need to be further investigated, despite the fact that the agriculture sector requires a lot of care and precision due to the direct impact it has on human health. The removal of HMs, inorganic and organic pollutants, along with the detection of contaminants in water, soil, and air are just a few of the diverse uses of BNMs in the environmental field. Numerous publications have solely concentrated on the

An Overview of Magnetic Nanomaterials


environmentally friendly synthesis of various metals and their applications in diverse fields. Innovative alternative methods to control pollution are now required due to the rise in both global warming and pollution. BNMs have made it feasible to produce solar cells to harness solar energy, bioremediation materials that can quickly deteriorate contaminants found in water and soil, and the creation of NBSs to identify pollutants. These BNMs are crucial in the treatment of wastewater that contaminates freshwater sources. Modernization and globalization have drawbacks that must be addressed as soon as possible. BNMs exhibit the ability to overcome these drawbacks and have a promising future. Acknowledgements The authors are grateful to their respective institutions and appreciate the authors and publishers whose articles were used for this chapter.

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Magnetic Nanomaterials: Synthesis and Characterization David O. Idisi, Chinedu C. Ahia, and Edson L. Meyer

Abstract Magnetic nanomaterials (MN) have gained popularity recently, due to their versatility in different applications in biomedicine and water splitting. Because of the ease of magnetic response to the applied field and manipulation of the itinerant magnetic moments, MN offers seamless opportunities in different science and technology. In this chapter, different MNs are examined with a focus on their syntheses and characterization. This chapter provides insight into the previously reported characterization techniques for morphology, microstructure electronic and magnetic properties examination.

1 Introduction Magnetic nanomaterials are an interesting subject to the research community due to the possibilities they offer. The ability to manipulate their morphology and particle size has led to the tuning of their spin alignment [1, 2]. The tuning of the spin alignment can be harvested for different applications. For instance, the saturation magnetism observed in ferromagnetic nanomaterials is crucial for soft magnet applications, allowing for ease of upscaling and miniaturization [3]. High coercivity and remanence of an MMO classify the material as a permanent or soft magnetic material. Because of the ability of the permanent magnets to distribute magnetic flux within the air gap of magnetic circuits [4], they have been prevalent in sensors, motors, actuator applications [5]. Low coercivity, and remanence forms soft magnetic materials, possessing single domain superparamagnetic materials. The control of the remanence and coercivity can be used in the manipulation of the rate of relaxation of magnetic imaging resonance (MRI) applications [6]. The control of the rate of relaxation enables the tuning of spin relaxation times emanating from latticespins (T1) and (T2) spin–spin interactions, which are applicable in image contrast control in MRIs [7]. D. O. Idisi (B) · C. C. Ahia · E. L. Meyer Fort Hare Institute of Technology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 U. O. Aigbe et al. (eds.), Magnetic Nanomaterials, Engineering Materials,



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2 Type of Magnetic Nanomaterials Depending on the nature of the nanomaterials, they can be classified as metallic oxide nanomaterials, metal alloy nanostructures and graphene oxide/metal nanocomposites. The synthesis process allows for control over the magnetic characteristics of the nanomaterials. This chapter will look at previously described synthesis methods and characterization methods for several magnetic nanomaterials. Firstly, each class of nanomaterials will be discussed. The process of the synthesis method for most of the classes of magnetic nanomaterials are similar, hence a general synthesis section will be considered. Since the characterization is common to most of the materials, a generic characterization section will be presented for all the magnetic nanomaterials.

2.1 Metallic Magnetic Oxides Metallic magnetic oxides (MMO) are a class of metallic materials with a high magnetic response (coercivity, remanence and saturation) and are chemically stable. However, their high reactivity results in their easy oxidation in air and water. For instance, iron nanoparticles (Fe-NP) easily oxidizes leading to the formation of iron oxide [8]. Although the degree of oxidation can result in decreased magnetic response and application limitations, additional metals can be introduced into the structure of Fe2 O4 to increase the chemical stability and magnetic response [9]. Among the numerous available metals, Co, Mn and Fe have been used, which results in improved magnetic properties. Enhanced magnetization and chemical stability are usually attributed to uncompensated surface spins and interface interactions between Fe and the metallic ions [10].

2.2 Metal Alloy Magnetic Nanostructures Magnetic metallic alloy nanostructures (MAN) involve the combination of two magnetic monometallic nanomaterials with the aim of improving their combined magnetic properties. MAN, which is represented by FePd and FePt nanomaterials, is chemically stable and highly magneto-crystalline [11]. The enhanced magnetization can be attributed to the exchange interaction between the valence orbital state. Previous reports [12] have attributed enhanced blocking temperature and coercivity to the degree of stoichiometric tuning of each mono-metallic nanoparticle. The ease of control of the particle size of the bimetallic nanomaterials can result in manipulating the magnetic features. For instance, Hou et al. [13] were able to obtain FePd nanoparticles in the size range of 11–16 nm, which exhibit superparamagnetic properties. Based on the enhanced magnetic features of the MAN nanomaterials, they have

Magnetic Nanomaterials: Synthesis and Characterization


found opportunities in different applications such as tissue imaging, drug delivery, and imaging-guided photothermal therapy [14].

2.3 Graphene Oxide/Metal Nanocomposites A derivative of graphene, which is referred to as graphene oxide (GO) has oxygen functional groups at its edges and basal planes [15]. The presence of the oxygen functional group allows easy attachment of metals to its matrix [16]. Pristine graphene is intrinsically nonmagnetic without localized magnetic moment resulting from the absence of unpaired spins [17]. However, the oxidation and reduction of the carbon atoms create hydroxyl and epoxy doping, resulting in the introduction of magnetic moments [18]. Meanwhile, the magnetization of GO has been widely enhanced with the GO-based nanocomposite and has shown enhanced ferromagnetic [19] and superparamagnetic properties [20], which could find potential in memory device and tissue imaging applications. Additionally, iron-based MMO nanoparticles have been incorporated into GO to enhance its magnetic properties. The coupling of the large surface area and enhanced magnetic properties of GO: Fe3 O4 nanocomposite has shown enormous potential for biomedical applications [21, 22].

3 Method of Synthesis The effectiveness in synthesizing the magnetic nanomaterials is crucial for obtaining high throughput nanomaterials. The methods can be used to manipulate nanomaterials’ size, shape, and chemical stability, which are crucial for achieving the desired qualities. The following section is focused on previously reported syntheses for MMOs.

3.1 Sol–Gel Method The sol–gel method involves the use of solution-based chemistry, where precipitate precursors are mixed with reagents/solutions in desired proportions to obtain highyield precipitates [23]. The process of separation, nucleation and growth of nanomaterials can be easily observed and monitored during the synthesis process. Figure 1 shows the typical steps involved in the synthesis of metallic magnetic nanomaterials. Iron oxide MMO is typically prepared by adding a base solution to ferrous salt under anaerobic circumstances at room temperature. This results in the production of Fe (II) and Fe (III) precipitates. The control of the shape, particles, and composition is usually manipulated using ferrous salt ratio, reaction temperature, medium pH and ionic strength of the solution [24].


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Fig. 1 Schematics representing the process of sol–gel synthesis of magnetic nanomaterials

The case of the use of sol–gel method for the preparation of CoFe2 O4 involves a process similar to that of Fe2 O3 . However, Cobalt(II) acetate tetrahydrate is added to the ferrous salt to create a Co: Fe atomic ratio to produce the desired precipitate [25]. Similarly, the main distinction for the case of MnFe2 O4 involves the use of manganese- (II) benzoyl acetonate as Mn precursor, which is mixed with a ferrous salt precursor in adequate proportion [26]. The effectiveness of the sol–gel method in preparing homogenous precipitate has been proven and is still widely used in the current era. Among the numerous study that has been devoted to the synthesis of magnetic nanomaterials using the sol–gel method, few articles have been considered. The early work of Deheri et al. [27] outlined the synthesis of Nd2 Fe14 B-based magnetic nanomaterials. The synthesis process followed a typical mixture of the material precursor in deoxidized water with a final yield of random dispersed 100 nm nanoparticles. The resulting composites are shown in Fig. 2. Additionally, Masthoff et al. [28] attempted a modification of the sol–gel method by implementing a nonaqueous approach. The distinction of their approach employed a Polyclave reactor and benzyl alcohol as solvent, which enabled the monitoring of the reaction process. Their results led to formation of faceted shaped magnetic nanoparticles. In general, the sol–gel technique is efficiency and can be modified with precursor to obtain desired shape and morphology of the nanomaterials.

3.2 Thermal Decomposition Organometallic precursors are broken down in organic solvents during the thermal decomposition process. To achieve high MMO throughput, capping agent surfactants are introduced into the surfactant under anaerobic conditions [29]. For controlling the particle size and form, reaction factors like temperature, reaction time, and ageing are essential [30]. Meanwhile, the use of the thermal decomposition method for the preparation of highly magneto-crystalline MANs has been widely explored [31, 32]. A previous report by Patsula et al. demonstrated the synthesis of Fe3 O4 -based MMO nanomaterials by decomposing Fe(III) glucuronate [33]. Temperature variation and reagent concentration were used to obtain stable nanosized superparamagnetic nanomaterial. In the process, the temperature, concentration of the stabilization agent

Magnetic Nanomaterials: Synthesis and Characterization


Fig. 2 TEM image of Nd2 Fe14 B-based magnetic nanomaterials, indicating randomly dispersion nanoparticles. Image adapted from Deheri et al. [27]; Copyright, ACS Publisher, 2010

(poly(3-Omethacryloyl-α-D-glucopyranose)) and high-boiling point solvent, polydispersed and nanosized particles were varied to produce the Fe3 O4 nanoparticles. Figure 3 shows the monodispersed Fe3 O4 nanoparticles using the thermal decomposition method. Meanwhile, Sun et al. [34] used the thermal decomposition method to prepare monodispersed Fe-Pt nanoparticles. The process of synthesis is similar to MMO preparation, however, octyl ether is used as the capping agent. The process results in 12nm-sized particles, which can exhibit superparamagnetic properties. While the thermal decomposition method is efficient for preparing monodispersed nanosized magnetic nanomaterials, it suffers some setbacks. For instance, toxic CO gases are generated during the preparation of Fe(CO)5 -based precursors [35]. The setbacks cause difficulty in nanomaterial synthesis. Hence, other precursors are either used or other methods are adopted. It is based on this issue; that thermal decomposition is becoming less popular for bimetallic nanostructural synthesis.

3.3 Hydrothermal Method The hydrothermal method of magnetic nanomaterial synthesis is a solvothermal method, which involves a heterogeneous reaction of inorganic precursors in solutions above room temperature (125–250 °C) and pressure (0.3–4 MPa) [36]. The reaction time and precursor concentration play a key role in regulating the nanomaterial’s


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Fig. 3 The morphology of the obtained Fe3 O4 nanoparticles using the thermal decomposition method. Image reproduced from Patsula et al. [33]; Copyright, ACS Publications, 2016

particle size distribution and shape [37, 38]. In order to create MMOs and graphene oxide/metal nanocomposites, the hydrothermal approach has been extensively used. For iron oxide based MMO nanomaterial preparation, ferrous chloride tetrahydrate precursor is used in the presence of ammonia hydroxide solution [39]. The vigorous stirring of the mixture leads to a formation of an oxidized iron II oxide precipitate. The iron oxide precipitate is transferred to an autoclave and heated at desired temperatures (120–150 °C) and pressure (2 bar). The case of graphene oxide/metal composite involves a two-step process as in the case of iron oxide based magnetic nanomaterials. The graphene content is prepared from the reduction of Modified Hummer’s synthesized graphene oxide [40]. The mixture of the synthesized and ferric chloride or nitride is transferred to a Teflon autoclave for the hydrothermal heating process. The heating and reaction process is similar to MMObased nanomaterials with similar monodispersed nanoparticles [41, 42]. Numerous research (see Table 1) on the hydrothermal synthesis of magnetic nanomaterials has been reported. However, for sake of simplicity, few reports have been considered in this section. The recent report of Makinose [43] explored ammonia-treated Fe-oleate precursor for hydrothermal synthesis of iron oxide nanoparticles. The impact of the ammonia-treated Fe-oleate precursor resulted in the production of high dispersive iron oxide nanoparticles. The effect of the Fe-oleate precursor suggests the ease of manipulating the structure and morphology of magnetic nanomaterials using the hydrothermal method.

Magnetic Nanomaterials: Synthesis and Characterization


Table 1 Summary of selected reports on the various magnetic nan Synthesis method

Class of magnetic nanomaterial



Metallic magnetic oxide, magnetic alloy nanostructure and graphene oxide/metal nanocomposites

[19, 20, 29, 54–59]

Thermal decomposition

Metallic magnetic oxide and magnetic alloy nanostructure

[33, 60–64]


Metallic magnetic oxide and graphene oxide/metal nanocomposites

[41, 65–69]

Other methods

Metallic magnetic oxide and magnetic alloy nanostructures


3.4 Other Methods The afore-discussed methods have been widely used for the synthesis of magnetic nanomaterials. However, other methods have been used in recent times, which are efficient in the preparation of high-yield magnetic nanomaterials. Other effective methods include polyol, microemulsion and green synthesis. The polyol method is a liquid-phase process used for extracting fine metals from oxides, salts and hydroxides using high-boiling and multivalent alcohols [44]. Due to the water-comparable and ionic bonding nature of the polyols class, nucleic coordinated magnetic materials can be synthesized [23]. Due to the nuclei’s surface and protective agent, which alters the crystal’s characteristics and allows for particle growth of related anisotropic particles, particle size and dispersion are also possible [45]. The polyol technique has been extensively investigated for the synthesis of high yield MANs and MMOs due to the simplicity of removing the glycol residues during post-synthesis. Recent studies of the method being used for the preparation of MANs and MMOs are indicated in Table 1. The microemulsion method is based on the formation of isotropicthermodynamically stable dispersion from two–three immiscible solvents. The resulting dispersion produces an interfacial layer with molecular surfactants [46]. Immiscible mixtures have an effect that causes hydrophilic head solubility in water and hydrophobic tail solubility in oil solutions, which are the factors that cause the monolayer interface to form [47]. When tiny droplets of water are continually dispersed in the hydrocarbon phase while being encompassed by monolayers of molecular surfactants, a water-in-oil combination is formed [48]. As a result, when two identical water-in-oil microemulsions are combined with the required reagents, the resulting microdroplets continuously collide, agglomerate, and degrade to form micelles precipitates. To remove the precipitate, the product is filtered or centrifuged in acetone or ethanol [49]. The microemulsion method allows the control of the particle size, shape and crystallinity by tuning the synthesis conditions Selected previous reports on the microemulsion prepared magnetic nanomaterials are given in Table 1.


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Green synthesis of magnetic nanomaterials involves the use of green chemistry in preparing the nanomaterials. Green chemistry has gained prominence mainly because of the call for a reduction in environmental toxicity. Increased research activity in nanomaterials synthesis for different applications has resulted in toxic waste by products, which are eventually dumped in the environment. The aftermath of the waste has led to different environmental hazards, which are harmful to both human and plant lives [50]. Magnetic nanoparticles are produced with the aid of plants as part of the green synthesis. Instead of actual chemical reagents, plant extracts are used as sources for citric acid, ascorbic acid, flavones, basic enzymes such dehydrogenases and reductases, and extracellular electron carriers [51, 52]. A typical green synthesis process involves mixing plant extracts with the desired solvent medium, reducing agent and capping agent for the reduction of agglomeration of nanomaterials [53]. Although green synthesis can help reduce toxicity in nanomaterial synthesis, it has not been popular among researchers due to some setbacks. For instance, the poor yield of naturally occurring plant proteins makes it difficult to attain desired particle size, shape, and crystallinity [23]. A summary of the synthesis method for the preparation of magnetic nanomaterials indicating some selected reports is depicted in Table 1.

4 Characterization of Magnetic Nanomaterials The characterization of magnetic nanomaterials gives insight into the inherent properties of the materials. Characterization of nanomaterials can enable possible optimization and enhancement of the properties as desired. This section of the chapter focuses on the characterization techniques used to probe the microstructure, morphology, and electronic magnetic properties of magnetic nanomaterials. The following details the different techniques used for probing the properties.

4.1 X-ray Diffraction The study of nanomaterials’ structural characteristics, including size, crystal defect, crystallinity, and strain, is made possible through X-ray diffraction (XRD). These characteristics can be utilized to comprehend the behavior of a nanomaterial that has been observed [75]. The XRD technique is based on Bragg’s Law of diffraction. The basis of the principle depends on the reflection/scattering of X-rays when a sample of crystal blueprint is bombarded with X-rays with precise wavelength at the incident angle. The reflected/scattered X-rays can be either constructive or destructive. The travelling wave’s path differences for constructive wave interference are integer multiples of the wavelength. When constructive interference occurs, a diffracted set of beam X-rays at an angle equal to that of the incident beam create a distinct blueprint of the targeted material [75].

Magnetic Nanomaterials: Synthesis and Characterization


The pattern obtained from the XRD diffraction experiment can be used to extrapolate much information about the magnetic nanomaterial. For instance, the XRD technique can be used to identify the crystal structure of magnetic nanomaterials. For graphene-Fe nanocomposite based magnetic nanomaterials, face centred cubic (FCC) structure can be easily identified from the reflection planes [76] obtained from XRD patterns. Furthermore, the interplanar spacing (d-spacing), which is unique to the desired nanomaterial, can be easily identified. The d-spacing between the lattice planes inherent in the atoms of the desired magnetic nanomaterial, which is responsible for the constructive interference, is indicated by the solution of Bragg’s equation. In general, nanomaterials with high symmetry have fewer atomic planes than those with low symmetry, which have more structural atomic planes [77]. One of the numerous reports on the XRD technique was performed by Liu et al. [31], where the focus was made on characterizing NiFe-based magnetic nanomaterial. The XRD characterization of the NiFe-based (see Fig. 4) nanomaterial indicated a face-centered cubic (fcc) type and spinel structure, which is consistent with typical fcc-type NiFe nanoparticles. Other selected reports regarding XRD characterization are indicated in Table 2 Fig. 4 XRD characterization of NiFe magnetic nanomaterials, showing the microstructure and phase of its electronic structure. Image reproduced from Liu et al. [31]; Copyright, Elsevier Publishers, 2014


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Table 2 Summary of selected previous reports on the different characterization techniques for magnetic nanomaterials Class of magnetic nanomaterial

Characterization technique


Metallic magnetic oxide

XRD, SEM, TEM, Raman spectroscopy, TGA, XPS, [31, 104–107] UPS, XANES, SQUID, VSM

Magnetic alloy nanostructure

XRD, SEM, TEM, Raman spectroscopy, TGA, XPS, [11–13, 34, 108–110] UPS, XANES, SQUID, VSM

Graphene oxide/ XRD, SEM, TEM, Raman spectroscopy, TGA, XPS, [19, 20, 111–114] metal UPS, XANES, SQUID, VSM nanocomposites

4.2 Scanning and Transmission Electron Microscopy Scanning electron microscopy (SEM) is a widely used technique for probing the morphology (particle size, shape, and texture), of nanomaterials at high resolution. The SEM technique uses an electron beam to scan the sample in a cross-sectionally manner. Under high vacuum conditions, signals and images of the scanned sample are generated and displayed on a cathode ray tube screen [78]. The high resolution of the technique enables the probing of up to 1nm with a high level of accuracy and resolution. SEM can be used with other peripherals such as laser diffractions, to probe particle agglomeration, which is crucial for understanding the behavior of the composites [79]. Furthermore, with the help of various advanced software, the generated images can be analyzed to obtain a histogram of particle grain sizes. Magnetic nanomaterials’ morphology and grain size boundaries have been extensively studied using the SEM technique [80, 81]. Meanwhile, this SEM technique has some disadvantages. For instance, the sample preparation for SEM measurements is time consuming. Furthermore, while it is easy to extrapolate grain size, particle size generation is challenging as the visual image does not provide quantitative information. The non-quantitative limitation is mainly due to the restricted area view that can be probed per time [79]. Transmission electron microscopy (TEM) on the hand is similar to SEM with the electron beams generated from an electron gun. The main distinction of TEM over SEM is the high resolution, which enables the probing of the inner structure of a sample. When the generated electron beams interact with a sample, the beams diffract in accordance with Bragg’s second law [82]. The diffracted beams are refocused by a magnetic lens, which results in the formation of an image. The generated image passes through a fluorescent screen where polychromatic images are recorded. Additionally, the image quality can be improved by considering the thickness of the sample layer. For instance, sample layers, which are approximately generated dark contrast images, whereas less thick sample layers result in bright images [83]. The SEM and TEM technique has been the main morphology characterization approach for studying the morphology of nanomaterials. Among the numerous morphology focused research,

Magnetic Nanomaterials: Synthesis and Characterization


Fig. 5 Morphology of cell coated iron oxide using SEM analysis. Image reproduced from Calero et al. [84]; Copyright, Elsevier Publishers, 2014

Calero et al. [84] studied the morphology of cell coated iron oxide using SEM analysis as indicated in Fig. 5. Their result revealed incubated cells within the iron oxide cell surface adherence to the iron oxide nanoparticles. Their report suggests the invaluable efficiency in studying the morphology of magnetic nanoparticles in the field of biomedicine. Meanwhile, Mohammadali et al. [85] in their report focused their study on the correlation of particle size of superparamagnetic iron oxide on different biomedical applications using TEM analysis. Figure 6 shows the TEM images and the corresponding particle analysis of the magnetic nanoparticles. Their results were able to show the significance of TEM in showing the morphology of magnetic nanomaterials as well as mean particle distribution within the nanomaterial. Other previous reports are summarized in Table 2.

4.3 Raman Spectroscopy The impact of doping or functionalizing nanomaterials is studied using Raman spectroscopy, as well as the bonding structure in molecules or solids. When incident light interacts with the desired sample, light is scattered, which is the basis of the Raman technique [86]. The inelastically scattered photons with wavelengths unequal to the incident light depict a blueprint of the chemical bonding of the sample. The detected


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Fig. 6 TEM images and particle size analysis of superparamagnetic iron oxide. Image reproduced from Mohammadali et al.; Copyright, Springer Publishers, 2020

signal from the scattered light is used to form a spectrum with a Raman shift peak and intensity, which is unique to the desired sample. The Raman spectra give two characteristics peaks at approximately 1585 and 2950cm−1 ( G and 2D) for a carbon-based nanomaterial. However, a defect peak (D peak) at approximately 1350cm−1 appears for a defect carbon nanomaterial, which could be due to oxidation, doping or functionalization [87]. The effect of doping/ functionalization changes the frequency of the vibration of the phonons, which leads to either a blue or redshift of the photon vibrations [87]. Additionally, iron oxidebased nanomaterials show Raman peaks between 200 and 1330 cm−1 depending on the nature of the magnetic iron oxides. For instance, hematite features peaks at approximately 225, 245, 291, 411, 500, 611 and 1321cm−1 [88], whereas, magnetite shows blueprint peaks at the range 661 and 676cm−1 depending the power and wavelength of the laser source [88]. The Raman technique has been widely used for characterizing magnetic nanomaterials and has been widely reported. One of such studies was our recent report [89] on SiO2 decorated multiwalled carbon nanotubes (MWCNT). In the report, we were able to quantify the impact defects resulting from the concentration of SiO2 nanoparticles on MWCNTs and its corresponding effect

Magnetic Nanomaterials: Synthesis and Characterization


Fig. 7 Raman spectroscopy of SiO2 nanoparticles decorated MWCNTs. Image reproduced from Oke et al.[89]; Copyright, ACS Publishers, 2019

on the magnetic properties. Figure 7 shows the Raman spectra of SiO2 nanoparticles decorated MWCNTs. Additional reports in the Raman characterization of magnetic nanomaterials are summarized in Table 2.

4.4 Thermal Stability Properties The process of nucleation resulting from the functionalization and oxidation of elemental components in magnetic nanomaterials can lead to clustering/ agglomeration of the particles. The effect of agglomeration in nanomaterials results in weakened nanoparticles, which makes the nanomaterials less effective for desired applications. A way of controlling the process of agglomeration is using thermal stability studies, where the volatile component and weight changes of the nanocomposites can be easily monitored. Additionally, thermal stability studies are crucial for magnetic nanomaterials for biomedical studies to monitor the impact of temperature and degradation of the magnetic nanocomposite resulting from the nanoparticles.


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Meanwhile, thermogravimetric analysis (TGA) has been the standard method for analysing the thermal stability of magnetic nanomaterials. The TGA technique is based on the enthalpy change in a thermodynamic system (nanocomposite), which relies on changing the temperature and mass of the entire system. In the TGA process, the mass of the nanocomposite is continuously monitored as the temperature is linearly increased over a range of 25–1200 °C. The setup includes a programmed furnace that records the experiment, and the spectra that were produced were used for data analysis of factors like absorption, adsorption, desorption, vaporization, sublimation, degradation, oxidation, and reduction. Based on the efficiency of the TGA technique in magnetic nanomaterial characterization, numerous reports have been devoted to the subject. For instance, Sivakumar et al. [90] studied the Nickel ferrite (NiFe2 O4 ) using TGA to establish the decomposition process. In their study, they found three decomposition regions (see Fig. 8), which gives insight into the adsorption activity of H2 O, CO2 and NOx in the NiFe2 O4 composite. Additional information is indicated in the summarized selected previous reports on the use of TGA for thermal stability of magnetic nanomaterials are indicated in Table 2.

Fig. 8 TG analysis of NiFe2 O4 composite showing the three decompositions at 50–150, 150–480 and 480–640 °C. Image adapted from Sivakumar et al. [90]; Copyright, Elsevier Publishers, 2011

Magnetic Nanomaterials: Synthesis and Characterization


4.5 X-ray Photoelectron Spectroscopy An enhanced method for analyzing the electronic chemical content, quantity, and bonding structure of materials is called X-ray photoelectron spectroscopy. The photoelectric effect provides a framework for the XPS method. Electrons are released from a sample’s surface when it is irradiated with a photon of a particular energy, often Mg K (1253.6eV with a line width of 0.85eV) or Al K (1486.6eV with a line width of 0.85eV) [91]. The signal detected from the population of the emitted electrons from the surface is recorded and used to form a spectrum with varying binding energies. The peak intensities and positions represent the elemental concentration and chemical composition of the material being analyzed. The chemical composition identification from the binding energy is based on a unique energy region where each electron is emitted from the surface [92]. The binding energy regions can be used to identify each element present in a sample. For instance, a spectrum showing peaks at a binding energy of 285.03 eV is attributed to carbon (C1s), 103.29 eV to silicon (Si2p), 83.98 and 87.7 eV are attributed to gold (Au 4f7/2 and Au 4f5/2 , respectively), and 532.68 eV to oxygen functional groups (O1s) [93]. Additionally, the impact of oxidation and functionalization of the material results in the splitting and broadening of the peaks. The ability to evaluate the orbital and spin angular momentum of the material’s electronic structural configuration makes the XPS technique effective at investigating the electronic structure of nanomaterials [94]. A typical electronic state comprises electrons with orbital and spin angular momentum. When an electron is emitted from the initial state through the absorption of a photon, the electron emerges with a kinetic energy of the final state with electronic subshell and unpaired electrons. Based on the nomenclature of the electronic state, the emerging electrons obey the quantum mechanics principle in accordance with nl j, which are the quantum number, angular momentum quantum number and combined spin, respectively. Hence, spin orbit coupling and splitting are observed in some elemental compositions such as Au 4f and Fe 2p, which possess a doublet state [95]. In summary, XPS has been widely used for in depth profiling of magnetic materials. The result of its use is reflected in the enormous number of research publications. For instance, our recent report [19] indicated a blue and red shift in peak positions of C–C, C-O, C-Au in C 1s and O 1s of rGO functionalized gold nanoparticles (see Fig. 9). The bond interactions suggest the possible attachment of Au atoms on the surface of rGO, which has a corresponding effect on the enhancement of the magnetic properties of rGO. Other significant contributions to XPS characterization of magnetic nanomaterials are indicated in Table 2.


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Fig. 9 XPS spectra analysis for gold functionalized rGO showing C 1s and O 1s. Image adapted from Idisi et al. [19] Copyright, Elsevier, 2019

4.6 Ultraviolet Photoelectron Spectroscopy Ultraviolet photoelectron spectroscopy (UPS) is a complementary technique to XPS, which involves the emission of electrons from an occupied orbital when illuminated with a photon source. The UPS technique comprises two helium photons with excitation energies of (He I = 21.2eV and He II 40.8eV). The helium sources enable the in depth probing of the different electronic transitions and states, which is inaccessible by the XPS technique. The obtained spectra from UPS can be easily assigned based on the available orbital state in a material. For a typical GO-based magnetic nanomaterial, the orbital states are in the range of 3−15 eV. For instance, the ranges 3−4 eV are assigned to 2p − π, 5−7 eV are assigned to 2p − (σ + π), 8−11 eV are assigned to 2p − σ and 13−15 eV are assigned to the 2s − σ state. The effect of reduction, doping and functionalization induce defect levels in the precursor materials. The resulting induced defects lead to an alteration in the electronic structure of magnetic nanomaterials. For instance, a typical reduced or functionalized GO-based nanomaterials will lead to either red or blue shift in the peak positions of the orbital states. The degree of the red or blue shift in the peak positions depends on the degree of reduction and the

Magnetic Nanomaterials: Synthesis and Characterization


concentration of the functionalizing agent [20]. Sutar and co-workers have extensively studied the effect of the reduction of GO on the orbital states using the UPS characterization technique. Additionally, the UPS technique may be utilized to investigate a material’s work function characteristics, which is essential for comprehending the electrical structure and chemical make-up of nanomaterials. By measuring the difference between the Fermi Level and the cut-off energy at the lower kinetic energy end of the spectrum and estimating the difference from the incident photon energy, the electronic work function may be retrieved from the UPS spectra [96]. Meanwhile, the process of probing the work function of a magnetic nanomaterial can be extended to the valence band maximum examination. The behaviour of the VBM provides an insight into the defect induced transport properties and valence state of constituent elements of materials. in magnetic nanomaterials. The VBM has been widely used to examine the active orbital states, which are responsible for the magnetic moment interaction in nanomaterials. Menzel and co-workers [97] used the UPS technique to elucidate the effect of Co on the magnetic properties of single crystalline Fe1−x Cox Si. Their result (see Fig. 10) showed a shift of valence band maximum towards the Fermi energy when the concentration of Co is increased. Other previous reports on the use of the UPS technique for probing work function and VBM are indicated in Table 2.

Fig. 10 UPS spectra of Fe1-x Cox Si single crystal composite. Image adapted from Menzel et al. [97]; Copyright, Elsevier Publishers, 2004


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4.7 X-ray Absorption Near Edge Structure Spectroscopy X-ray Absorption Near Edge Structure (XANES) is an advanced electronic characterization, which uses inner shell excitation to probe the final electronic states that can be either unoccupied or partially filled. The XANES technique is element-specific and examines local bonding-sensitive structures in nanomaterials. The XANES technique is based on the absorption of photon ionization by an electron, which leads to the formation of an empty state from a core level [98]. When the photon energy is equal to or greater than the binding energy of the core-level, an electron in that core is activated. When the photon energy is probed, the excitation results in absorption edges. Therefore, the energy of an absorption edge matches the energy at the core level, which is particular to each element. The absorption edge in the XANES spectrum and associated energy counts in the vertical axis are produced by the enhanced absorption energies corresponding to the absorbed core electrons. The quantum number theory is also used to describe how the absorption edges are categorized. K edge [1s], L edge (2s, 2p), M edge (3s, 3p, and 3d), and N edge (4s, 4p, 4d and 4f) are few examples. Pre-edge, main edge, and post edge are the three sections that make up a typical XANES spectrum. The local symmetry of the relevant atom is said to be responsible for the pre-edge. The post edge is linked to interactions between the parent atoms and surrounding atoms from doping and functionalization, whereas the main edge is caused by the effect of the oxidation of the localized bonds inside the atoms [99, 100]. XANES spectrum data can be analyzed to probe the elemental content within a composite. In the analysis, the XANES spectrum is fitted with a Gaussian function to extrapolate an area under a curve. The area can be integrated to quantify the elemental content. The analysis can be applied to study the impact of nucleation resulting from doping/functionalization in heterostructures. The use of XANES in probing the electronic structure of magnetic nanomaterials is very efficient and has led to different reported studies. A previous study by Gyergyek et al. [101] examined the electronic structure using of cobalt ferrite nanoparticles using XANES. Their results indicated contributions from Fe3+ valences, which have a corresponding influence on the obtained magnetic properties. of cobalt ferrite heterostructure. Additional significant previous reports on the use of XANES for the characterization of the electronic properties of magnetic materials are indicated in Table 2.

4.8 Magnetic Hysteresis Loop Measurements Magnetic hysteresis measurements are crucial to understanding the magnetic features of nanomaterials. The features can range from magnetic transitions, remanence, coercivity and saturation magnetization. These features can be used to classify the magnetic types and their possible applicability. The two main magnetic characterization devices comprise a superconducting quantum interference device (SQUID) and

Magnetic Nanomaterials: Synthesis and Characterization


vibrating sample magnetometry (VSM). The principle of the SQUID technique is based on superconducting Josephson junction and flux antenna. Although the SQUID technique is very responsive to weak magnetic fluxes, it suffers some set-back. The SQUID technique lacks sensitivity to magnetic fields, owing to the minute area of sample interaction [102]. The issue associated with the low magnetic field sensitivity results in a limitation to large-scale applications. Vibrating sample magnetometry, on the other hand, is based on the principle of Faraday magnetic induction. The change in the magnetic field, as proposed by the Faraday law, leads to the generation of an electric field. The generated electric fields can be used to probe the changing magnetic field in a magnetic nanomaterial. The working principle of the VSM technique involves vibrating a magnetic-based material that possesses a uniform field, resulting in the generation of electric current from the sensing coils. In a situation when a sample is well aligned at certain angles and undergoes a mechanical sinusoidal motion within the sensing coils, a magnetic signal is generated. The magnetic signal is represented in the form of a hysteresis loop, which can be used to classify the nature of magnetization and strength of the nanomaterial. The nature of the magnetization of a nanomaterial can be classified based on the parameters such as susceptibility, magnetic saturation, remanence and coercivity. Susceptibility measures the degree of the magnetic response of material by exploring the ratio of the magnetization M to the material to the applied magnetic field. Saturation magnetization refers to a state of magnetization where the applied magnetic field does not affect the magnetic response of the nanomaterial. Other parameters such as remanence and remanence are quantities used in qualifying the class of the magnetic nanomaterial. For instance, depending on the magnitude of the remanence and coercivity, the material can be classified as either a soft or hard magnet. Furthermore, the magnetic phase transitions of the magnetic nanomaterial can be established by exploring the magnetization vs temperature relationship. The obtained trend from the M-T curve can be used to predict the mechanism behind the magnetic type. Generally, the VSM and SQUID setup has proven effective in establishing the magnetic properties of different classes of magnetic nanomaterials and one out of the numerous reports on SQUID/VSM-based measurements was is presented by Ikram et al. [103]. Ikram et al. used SQUID measurement to show the impact of Tb3+ and Dy3+ concentration on the magnetic properties of CoFe2 O4 heterostructures (see Fig. 11). Their report was able to extrapolate magnetic parameters such as magnetocrystalline anisotropy constant, Coercivity Hc and Bohr magneton µB. These values provide crucial insight into the magnetic behaviour and potential for different applications. Other selected previous reports which outline the magnetic properties of nanomaterials using SQUID/VSM are summarized in Table 2.


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Fig. 11 Magnetic hysteresis plot of CoFe2 O4 heterostructure using SQUID magnetometer. Image adapted from Ikram et al. [103]; Copyright, Elsevier Publishers, 2020

5 Conclusion Magnetic nanomaterials are important for different applications such as memory devices, ferroelectrics, biomedicine and therapeutics. These applications are based on the manipulation of particle size, morphology and structure. Hence, the synthesis and characterization techniques used in studying magnetic nanomaterials are crucial. The importance of magnetic nanoparticles is examined in the current chapter, which also discusses various synthesis processes and strategies for characterizing them. The synthesis method focused on sol–gel, hydrothermal and green synthesis approaches. The characterization properties focused on the microstructure, morphology, electronic and magnetic properties of magnetic nanomaterials. The summary of a previous report on the class of magnetic nanomaterials with their synthesis method and characterization is presented for easy reference. In general, this chapter will give a summary of available magnetic materials and their properties, which can be informative for the material science research community.

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Utility of Magnetic Nanomaterials for Theranostic Nanomedicine Uyiosa Osagie Aigbe, Robert Birundu Onyancha, Kingsley Eghonghon Ukhurebor, Benedict Okundaye, Efosa Aigbe, Omamoke O. E. Enaroseha, Kingsley Obodo, Otolorin Adelaja Osibote, Ahmed El Nemr, Luyanda Lunga Noto, and Harrison I. Atagana

Abstract A leading cause of global death is cancer; hence its early detection and treatment are crucial. With the evolution and development of nanomaterials (NMs), there has been an amplified study on the advancement of modern detection and treatment methods using magnetic nanoparticles (MNPs’) with theranostic (TC) potential as nano-medicine for cancer treatment. Recent research in nano-medicine has begun U. O. Aigbe (B) · O. A. Osibote Department of Mathematics and Physics, Faculty of Applied Sciences, Cape Peninsula University of Technology, Cape Town, South Africa e-mail: [email protected] R. B. Onyancha Department of Technical and Applied Physics, School of Physics and Earth Sciences Technology, Technical University of Kenya, Nairobi, Kenya K. E. Ukhurebor Department of Physics, Faculty of Science, Edo State University Uzairue, Edo State, Nigeria B. Okundaye Centre of Urban Design, Architecture and Sustainability (CUDAS), Department of Architecture and 3D Design, School of Arts and Humanities, University of Huddersfeld, Queensgate, Huddersfeld HD1 3DH, UK E. Aigbe Department of Electrical and Electronic Engineering, Nile University of Nigeria, Abuja, Nigeria O. O. E. Enaroseha Department of Physics, Delta State University, Abraka, Nigeria e-mail: [email protected] K. Obodo Faculty of Engineering, HySA-Infrastructure, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa National Institute of Theoretical and Computational Sciences, Johannesburg 2000, South Africa A. El Nemr Environment Division, National Institute of Oceanography and Fisheries (NIOF), Kayet Bey, Elanfoushy, Alexandria, Egypt L. L. Noto Department of Physics, College of Science, Engineering & Technology, University of South Africa, Pretoria, South Africa © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 U. O. Aigbe et al. (eds.), Magnetic Nanomaterials, Engineering Materials,



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to explore the diagnostics and treatment combination (TC) as a technique to offer further adaptable, individual, and specific care for cancer treatment to better patient results. MNPs’ have shown huge potential in this regard, as they have become key candidates to be employed in a TC platform to achieve this concept of total cancer treatment in humans owing to their extra benefit of being remotely identified and controlled by utilizing a peripheral magnetic field (MF). Keywords Theranostic · Therapy · Cancer · Magnetic nanomaterials · Diagnostic

1 Introduction Comprehensive health care budgets have been growing abruptly over the past decade, but there has been a remarkable decrease in disease-related fatalities to permit such a severe cost increase. There has been a conceptual shift in the management of disease and clinicians are steadily moving from the conventional one drug fits all technique toward the concept of individualized medicine-the correct drugs for the right individual dispensed at the proper time [1]. A prominent cause of loss of life and a wide-reaching health problem is cancer. It is projected that by 2018, new cases of cancer and related death by cancer will be between 18.1 million and 9.6 million. It is a disorder that is typified by the uninhibited proliferation of cells that expand from an early central point to other sections of the body and thereby resulting in human death. Hence, it’s early detection and treatment to decrease its spread and mortality are paramount [2]. Cancer shows different capabilities and hallmarks, which include avoiding growth suppressors, cell death resistance, proliferative signalling sustenance, supporting replicative immortality, stimulating angiogenesis, and triggering metastasis and incursion [3]. While cancer is a leading reason of death, treatment choices are relatively limited and, in most cases, precise diagnosis and prognosis are complicated. Hence, great attempts in biomedical study have been dedicated to refining the sensitivity and precision of the diagnosis with the objective of early on identification and improved effectiveness of the techniques used for therapy [4]. Traditional NPs systems have been utilized in the past to attain disease administration distinctively. To satisfy all the required purposes, which bring matters of compliance and protection of patients into focus by various administrations, the TC NPs system has been developed to execute all facets of disease management in a particular setting [5]. The current medical treatment employed is chemotherapy, surgery, treatment via radiation, targeted treatment, hormone treatment, as well as green treatments like immune, cell and palliative treatment. Presently, the drawbacks of cancer treatment H. I. Atagana Institute for Nanotechnology and Water Sustainability (iNanoWS), College of Science, Engineering & Technology, University of South Africa, Pretoria, South Africa

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via clinical, immune-treatment, cell treatment and palliative treatment include their noxiousness, side effects as well as the present issues of specific or numerous drugresistance. Hence, the development of targeted therapy, which was capable of accomplishing precision, efficacy, and success at the cellular and molecular level to decrease impairment and noxiousness to regular cells is imperative and has progressively become the conventional treatment for cancer [3]. In the medical management of cancer patients, a critical issue has been the cancer resistance development to chemo- and radiotherapy. While advancement has been made in the identification and therapy of cancer, the survival of tumour patients remains at a low level-slung, mostly for patients detected at the subsequent phase. Hence, there is an imperative requirement for the advancement of sensitive diagnostic and efficient therapeutic (TRC) procedures for the development of a cancer diagnosis in patients [6, 7]. The development and improvement in the detection and treatment of diseases to a huge extent have been the focus of medical research [8]. Hence, a compelling purpose exists for the analytical and TRC agents creation, which was aimed at specific molecular targets, which can affix themselves to these targets and amass in the designated parts of the organism as well as techniques for their movement across the body. Also, they should have high sensitivity to outside stimuli to increase the management of their movement and their rate of release from their carriers. Application of the aforementioned needs an elaborate and valuable complex of various biochemical and biophysical knowledge platforms. At the turn of the millennium, a new paradigm and term “TCs” was developed as a complex solution to the above-mentioned problem. The phrase “theranostics-TCs” derived from the combination of the words “therapy” and “diagnostic” was first proposed by John P. Funkhouser from PharmaNetics, Inc. in 1998 [9]. TC NPs have gained increased consideration for the management of disorders in current times due to their instantaneous delivery of both imaging and TRC agents. The management of disorders involves the high specialized identification and diseased cell treatments as well as drug delivery process monitoring and TRC effectiveness [5]. The disease specificity and selectivity annihilation can be enhanced by the utilization of peripheral activatable TC agents to create concentrated cytotoxicity with not enough collateral harm. The capability to manage drug dosing in terms of location, time and quantity is a critical goal for the science of drug delivery, as enhanced management increases TRC impact while reducing side impacts [1]. The worldwide fad to enhance the effectiveness, techniques multi-functionality and safety and processes being created for biomedicine (BMD) through different convergent nano-technologies is more obvious. This method is targeted at eradicating various crucial constraints characteristic of conventional techniques for diagnostics and therapy. The highly widespread and consistently utilized techniques of contemporary medicine are incapable to identify cancer precisely at the initial stage. Also, tailored treatment is taken into account by the inherent particularities of a specific patient and is out of the reach of many individuals as the techniques regularly utilized lack sensitivity while unique ones are exceptionally pricey. Also, the action of the


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drug used is not confined, leading to the prospect of side effects, which increase with the therapy cost [9]. Lately, a new role is being played by nanotechnology (NT) in the biomedical sciences by offering various platforms of NT [4]. To prevail over fundamental restrictions in traditional methods that would allow for more useful and better infection identification and therapy, there has been intensive utilization of NT in medicine (nanomedicine-nmed). It also plays a critical role in the tailored treatment methods, which are useful for disease treatment with unpredictable representations among individuals and confronting the patient’s unpredictable TRC responses. This is ascribed to the NMs’ exclusive physical, biological, and chemical attributes when compared to their bulk equivalents. MNPs are of particular applicability in nmed owing to their extra benefit of being remotely detected and controlled by applying a peripheral MF [8]. Owing to their distinctive properties, MNPs have become the engine in the TC nmed field and can be employed in current imaging approaches like magnetic resonance imaging (MRI) and X-ray Computed Tomography (CT) and in developing analytical techniques like Photoacoustic Tomography and Fluorescence Molecular Tomography. With regards to treatment, they are mostly preferred for applications in drug delivery owing to their huge variation in shape, nature, structure and functionalization or surface coating [10]. The applications of MNPs involve their utilization as probes for examining disease status and problem mitigating through drug delivery. They have also been effectively utilized in the biosensor, fluorescent-magnetic bioimaging probe model and drug delivery nanocarrier synthesis. Specifically altered MNPs have also been employed for cancer detection and circulating tumour cells (CTCs) as well as the detection and attachment to the cell membrane receptors [11]. The objective of this chapter is to look at existing literature on the development and capability of MNPs in the identification and treatment of cancer in patients employing MRI, photothermal treatment (PTT), magnetic hyperthermia (MHT), and photodynamic treatment (PDT), as well as their blends. Figure 1 illustrates MNPs’ applications for the identification and treatment of cancer.

2 Routes for Iron Oxide Magnetic NPs (IOMNPs) Synthesis A state-of-the-art tendency in material science is to customize and put together conventional products with manipulated properties for specific applications [12]. For application in BMD, NT has improved the structures and design, obviously the important MNPs requirements and properties. Their popularity has increased and appeared as critical biomedical functional NMs owing to their extraordinary features like biocompatibility, high saturation magnetization, lesser noxiousness, chemical stability, and the capacity to work at the cellular and molecular echelons. They are utilized for the delivery of genes, delivery of drugs, diagnosis, chemo-treatment, photo-treatment, imaging mechanisms, and biosorption due to their inimitable features and in combinable techniques for TCs. Extensive variability

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Fig. 1 The application of MNPs for cancer diagnosis and treatment

of NMs has been utilized for improved contrast agents (CAs) encapsulation, TRC payloads biocompatibility and transportation and providing functional groups to couple biomolecules to improve MNPs efficiency employed for TC applications [13]. Inorganic NPs have added distinct and diverse material properties subject to their size and structure when associated with organic NPs [4]. MNPs have unique importance in the basic theory but have a broad array of functions in the BMD field. These magnetic materials are mostly magnetic combined materials comprising of ferromagnetic elements like Fe, cobalt, nickel or their oxides and alloys [3, 5]. Different types of materials that are magnetic are employed for the synthesis of MNPs and the main task is getting NPs that are stable in natural environments, are non-noxious and show the required magnetic properties. In biological media, sturdy magnets of rare earth elements are not chemically stable and are toxic to cells. While pure metallic magnets are disposed to deterioration. Hence, one of the easiest ways out is the use of iron oxide NPs (IONPs) like magnetite Fe3 O4 or hematite (Fe2 O3 ), which are non-noxious, and extremely biocompatible [11]. IOMNPs are generally created in the nano-dimensional rule and huge-sized particles that are magnetic show remanent magnetization (Mr) and coercivity (Hc ) values because of their multiplex-domain composition attributed to various crystallite positionings as depicted in Fig. 2. But with the sizes of particles decreasing to a regime of sub-micron (nanometernm), the multiplex-domain composition will get transformed into a single-domain structure and the value of Hc enhanced to the extreme. The decreased nm size at which the single-domain composition of these particles is defined as the singledomain dimension with a detailed analytical radius (rc ). With the further reduction in the magnetic particle size, these particles will possess superparamagnetism and this decreased size is known as the superparamagnetic (SP) size, which is generally in the size array of 4–20 nm for Fe3 O4 /Fe2 O3 NPs at ambient temperature. SPIONs


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Fig. 2 Graphic illustration of the variation in the coercivity with the MNPs size. [14] Adapted from Akbarzadeh et al.; Copyright, Springer Nature, 2012. Reprinted with permission from Springer Nature from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY)

specifically Fe3 O4 NPs have a transposed spinal crystal composition made of divalent Fe (Fe2+ ) and trivalent Fe (Fe3+ ) ions at the octa-hedral locations and a single trivalent Fe (Fe3+ ) ions at the tetra-hedral locations. The O anions (O2− ) are assembled amongst the Fe ions to create a closed-filled range of cubic formations in Fe3 O4 and maghemite (γ − Fe2 O3 ) NPs. For γ − Fe2 O3 , it has a comparable spinel structure to Fe3 O4 , with the single variation being that all Fe ions are in the trivalent form (Fe3+ ). Owing to the unmatched or unpaired 3d electrons in Fe3+ /Fe2+ cations’ presence in their crystal composition, the magnetic moments in SPIONs stem from. But these cations are situated far away from each other to stop their interaction or magnetic moment formation. Yet, through the nonmagnetic O2− , there is an interchange link between the cations resulting in the creation of magnetic moments [15]. The magnetization directions of MNPs are aligned along the direction of the field to realize magnetic saturation with a total magnetization reached when they are placed in an external MF. While the susceptibility determines the ease at which MNPs can be aligned. The strength of the field decrease leads to a specific level of reduction in the magnetization owing to the magnetic relaxations (MXs), thus their magnetization direction tends to be maintained and have a residue magnetization at a null field strength. When ferromagnetic NPs size is decreased to a point where the thermal energy (TE) is equal to the magnetic anisotropy energy, the NPs become magnetically unpredictable and are said to be SP. MNPs in an SP form have extremely feebler magnetic-dipole interactions and hence they are effortlessly strengthened and dissolved in an aqueous solution [16]. The key magnetic factors important to the TC usage are the Mr (the remanent magnetization after the peripheral MF is removed), Hc (defines the reverse MF strength required to take remanent magnetization to zero), Curie temperature (Tc ), saturation magnetization (Ms ) (the optimum proportion of material magnetization that can be attained under the external MF influence), blocking temperature (TB ), and anisotropy energy density (K) (the property of the

Utility of Magnetic Nanomaterials for Theranostic Nanomedicine


material that suggests the inclination of the magnetization to turn along a positive particle axis). These factors are impacted by the material, size, core–shell (functionalization), composition and shape of the NPs. As the particles’ volumes reduce, the NPs’ magnetic anisotropy energy (KV) diminishes also. Decreasing the particle size beyond a certain significant size will result in a specific magnetic domain creating a huge spin known as “super spin”, which leads to a huge magnetic moment on an individual particle (~10,000 Bohr magneton). Above the characteristics temperature (TB ), the SP behaviour is very comparable to a paramagnetic material [17]. MNPs comprising of Fe oxide (Fe3 O4 or Fe2 O3 ) and gadolinium (Gd) (complexes of chelated organic Gd) have greatly been exploited as CAs in MRI owing to their capability to separate into Fe and oxygen (O) inside the human body and can be removed securely and employed for metabolic and system transportation of O. When they are synthesized into NPs of 10 nm diameter, IONPs start to show SP behaviour, which leads to enhanced dispersive properties in MF absence and this is of prodigious importance in the application of objective drug delivery [5]. MNPs show non-lasting magnetism and this type of magnetism is currently primarily utilized to research the MNPs’ function in vivo. They have detailed substantial surface areas and can hold a range of proteins, miniature molecules, Ribonucleic acid (RNA), etc. Their magnetic properties enable their enrichment and separation and their movement and position in directions. Also, they have a magnetocaloric impact in an elevated frequency MF, which ultimately destroys tumour cells [3]. Notably, the application of MNPs in BMD is impacted by the composition and size of the IO. For angiography and tumour permeability applications, extrememodest SPIOMNPs are desired. Modifications in IO particles’ size and shape are considered by the substantial changes in the proportion of relaxation constants. These factors impact their heating-producing power, plasma half-life and bio-distribution, and determine their usage. These are the motives for the classification of the artificial techniques for MNPs synthesis as a function of the particle’s size (very modest, intermediate and huge particle) and shape (anisometric and spherical) [18]. The MNPs’ chemical, magnetic, and physical properties vary immensely on the technique of synthesis and their surface alterations and with considerable development made in the direction of MNPs’ shapes, composition, core–shell shape, and size variation [17]. Special consideration should be given to the preparation techniques that permit particle synthesis with practically unchanging dimensions and structure. This objective can be accomplished by the precipitation of a consistent solution under precise terms or by manipulating the growth of the particle through a process where a precursor in vapour or aerosol form is putrid. In the instance of MNPs application in BMD, their synthesis techniques are grouped into those that create MNPs’ from solution methods or vapour or aerosol forms and composites formed that consist of MNPs that are dispersed in submicron-sized inorganic or organic substances that generally have a spherical form. Another set of techniques that will be discussed for MNPs synthesis employs size range standards to create standardized NPs set out from polydisperse particles [12]. Substantial energy has been devoted to the strategy and production of MNPs that are ferromagnetic with precise parameters [13].


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The methods used for the production of MNPs’ can also be categorised into chemical, biological and physical procedures [19]. Aerosol/vapour-phase, flow injection, coprecipitation, oxidation, sol–gel, sonochemical decomposition, electrochemical, microbial, gas-phase deposition, herbal plant extracts (biosynthesis), thermal putrefaction or reduction, laser-pyrolysis, and hydrothermal methods facilitates MNPs synthesis via the chemical methods. MNPs are effectively formed by the solution phase using chemical methods, owing to the precise impact on the size, structure, and composition of MNPs. While the physical methods utilized for the synthesis of MNPs include laser-induced pyrolysis, gas-phase deposition, laser ablation, highenergy ball milling, aerosols and electron beam lithography [20]. The physical production approach persists due to the mechanical grinding down technique, pyrolysis, or thermal quenching. For the mechanical grinding down technique application, mechanical force is placed forward employing a universal ball mill to convert the starting material into particles that are nanosized. While thermal quenching is an approach which joins a quick satiate method to create amorphous elements with precise size crystallization using the thermal method. The pyrolysis approach employs high-pitched pressure precursors that are carbon-based gas or liquid, which are forced via an opening, to produce oxidized MNPs when burned into ash. These techniques make up an extensively recognized method deemed to be a sustainable alternative in terms of mass fabrication. Issues relating to size distribution uniformity can evolve and compromise the performance of MNPs’ employing these techniques [21]. Biological methods of MNPs synthesis consist of fungi, bacteria, or protein and microbial facilitated methods. These methods are effective owing to the simplification of NMs’ mass production and improved purity, but they do not offer superior management of the shape and size of NPs. The methods are further grouped into non-aqueous and aqueous routes, with the water-soluble (aqueous) route being highly preferred to the non-water-soluble route owing to sustainability and low cost. Figure 3 shows MNPs with suitable exterior chemistry applying the different synthesis methods [20]. MNPs creation through the physical techniques involves the magnetic responsive materials decomposition to target the preferred locations. Owing to their high energy requirements, experienced workforce and adjusted complicated factors for

Fig. 3 MNPs with suitable exterior chemistry, applying the different synthesis methods. [20] Adapted from Aigbe, and Osibote; Copyright, Springer Nature, 2022. Reprinted with permission from Springer Nature

Utility of Magnetic Nanomaterials for Theranostic Nanomedicine


their process, these techniques are problematic. While biological techniques are unique and highly focused, such that they comprise of magnetosomes in highly specified lipoprotein compartments that exist within the existing body [13, 22]. This allows the host to create MF inside it that reacts to the earth’s MF. The extremely resourceful technique that facilitates exceptional handling of NPs morphology, shape and size is the chemical technique. These techniques are modest and extremely productive and can be carried out devoid of any complex instruments. They are also eco-friendly and can effortlessly be scaled up for huge NPs production when equated to the other approaches. Simple dispersity in NPs with tunable dimensions is crucial for biological and bio-medical uses. The major task in the MNPs preparation using these techniques for TC uses is to regulate the NPs distribution, size, magnetic properties, surface chemistry and shapes. In vivo uses, any chemical or biological techniques are employed to synthesise magnetically sensitive NPs. But physical methods have also been utilized for NPs production employed for in vitro purposes like catalytic events and metallurgical procedures and numerous other manufacturing processes [13]. One of the all-purpose MNPs authorized by the Food and Drug Administration (FDA) for biomedical purposes like disease diagnostics and treatment is SPIONs [15, 23]. But a detailed research is needed to employ these SPIONs efficiently for TC purposes under scientific situations. Hence, scientists are perfecting the techniques for their synthesis to get superior characteristic SPIONs with excellent colloidal stability, narrow size distribution and superior magnetization. The hydrolytic and non-hydrolytic synthesis chemical paths are extensively employed for the production of superior characteristics SPIONs. hydrolytic synthesis methods are employed as traditional paths to precisely produce hydrophilic SPIONs centred on the chemical reactions with Fe precursors in water-soluble environments. Furthermore, produced SPIONs through hydrolytic techniques are further applicable for their direct biomedical uses. The key artificial paths used for the synthesis of SPIONs are hydrothermal, co-precipitation, sonochemical, thermal decomposition and microemulsion techniques [15, 17]. MNPs are employed as nano-carriers for drugs, CAs for imaging in MRI, magnetic targeting and local HT. But due to their superior surface-to-volume proportions and Van-der-Waals forces, opsonization is activated and poses a key barrier to their application in BMD [24]. For biomedical applications, NPs stability is a key critical feature, and the modification of their surface enables their stability and biocompatibility. They are of great importance as CAs owing to their SP activity, extremely minimal cost and biocompatibility which facilitate their easy use by researchers. For inorganic NPs, aggregation and oxidation are observed. Further modifications of their surface with various inorganic molecules, polymeric and nonpolymeric and ligands stabilizers provide a prospect for their application for various purposes and prevent actions such as aggregations, and sedimentation [25, 26]. IONPs that are functionalized are prospective contenders for bio-medical applications owing to their special chemical and physical properties. For their TC use, MNPs should have suitable monodispersity and basic size, high Ms, and appropriate hydrodynamic diameter. They should also have excellent consistency in an organic


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liquid medium, biodegradable and biocompatibility with reduced noxiousness and the capacity of clearance from the human body [6, 13]. The highly organic watersoluble solution are nonaligned, hence, MNPs coated with surfactants and polymers inhibit aggregation with reduced dipole–dipole interaction among particles, gravitational settling, enhanced biocompatibility and enhance surface functionality [13, 25, 27]. To enhance the stability of a colloidal, techniques employed include the use of polymers and surfactants (organic species) and silica or carbon (inorganic species) to coat NPs [19]. IONPs alterations with organic materials are carried out through in-situ, adsorption, and post-synthesis coating techniques. Organic and inorganic materials play a role as MNPs stabilizers by attaching covalently to the NPs to facilitate these particles to acquire high-level magnetic susceptibility. IONPs are altered with outstanding groups for enhanced functionalization through the add-on of various biologically functional molecules, thereby ensuing in organic or inorganic complexes that have a core/shell nano-structure for various functions. Harmful cell therapy via the immune system is extended with the addition of functionality and these functional complexes possess properties for TC applications which can be utilized in the medicinal and diagnostic processes. Also, the chemistry of core/ shell nano-structure surfaces determines their function and operational environments. Their overall noxious ness and response to pH are dependent on the surface modification which bring exact change in IONPs behaviour and by tuning the core size, coating thickness and target ligands, the nanoprobes designed are employed for specific cells, tissues and several disease biomarkers targeting [13]. Besides surfactants/surface coating molecules shielding SPIONs from aggregation, they also play a critical part in conjunction with the reactants in ascertaining the magnetic and physicochemical properties during the synthesis process. Besides, these molecules employed for surface coating allow for efficient functionalization or bio-coupling through the sway of appropriate functional surface groups to enhance their biocompatibility (decreasing noxiousness) and improving hydrophilicity (dispersibility of water) for the effective utilization of SPIONs for instant applications in biomedicals. The SPIONs stabilization is primarily reliant on the balance between the repulsive and attractive interactions, and the TE contribution. To deter aggregation, the typical NPs diameters can be assessed by employing Eq. 1 which associates the TE with the dipole–dipole pair energy. It should be noted that the magnetic interaction will decrease when D ≤ 10 nm (KB , T, B and uo represent Boltzmann’s constant, overall temperature, magnetization intensity and free space permeability) [15].  D≤

72KB T πuo M2

1/3 (1)

Biocompatibility is attained, with the coating stopping off any noxious ion seepage from the magnetic-core into the biological environment as well as the magnetic-core safeguarding against corrosion and oxidation. Also, the specific surface coating can

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stop protein adsorption, thereby improving the circulation time in the blood and boosting the possibility of the NPs getting to their target tissues [17]. In the succeeding sub-sections, the state-of-the-art synthesis techniques utilized for the preparation of MNPs for medical application will be described.

2.1 Thermal Decomposition Technique A key non-hydrolytic production method is employed for the hydrophobic SPIONs with regulated magnetic properties and physicochemical properties like shape, crystal structure, size, and composition [15, 22]. In thermal decomposition method consist of the organometallic Fe precursors decomposition in natural solvents at elevated temperatures. Though this technique can synthesize mono-dispersed particles of elevated quality owing to the distinct nucleation and growing process, it is a complicated process that creates hydrophilic NPs not usable openly for biomedical applications without a painstaking post-synthesis process and might likely result in magnetic properties loss and agglomeration [17]. This technique is founded on Fe precursors decomposition with or without surfactants’ presence in an elevated boiling-point natural solvent by heating them at an extremely elevated temperature range of 200–350 °C. To avoid superfluous IO phases, the decomposition of the precursor happens owing to the chemical bonds splintering through an endothermic reaction. SPIONs magnetic and physicochemical properties can be exact by the optimization of precursors/surfactants quantity, time of reaction and temperature of the reaction [15]. It is an up-scalable, laggard production technique that is utilized for non-magnetic organometallic precursors in the presence of an organic solvent. The organometallic precursors are derived from clean metal that is oxidized at 100–350 °C and the oxidative medium and thereby forms Fe oxides. Metal acetylacetonates or carbonyls are some of the present metal precursors utilized in this technique and fatty or oleic acids are the preferred surfactants also used for this method [21]. These techniques have various advantages over traditional methods due to the specific size and shape, superior crystallinity and thin particle size distribution control. But non-polar solvents and various non-biocompatible surfactant utilization have led to scepticism in the medical community for their appropriateness in biomedical applications [18]. Since SPIONs created using this technique are hydrophobic and cannot be used directly for tumours treatment, however, surface change methods such as ligand exchange or bilayer surfactant stabilization addition are needed to change the surface of SPIONs’ hydrophobic nature into hydrophilic nature. Currently, the one-pot thermal decomposition technique employing polyol-based surfactants has been utilized broadly to openly create hydrophilic SPIONs for cancer TC use [15].


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2.2 Microemulsion Technique A microemulsion is a visually translucent and thermodynamically stable solution, that is grouped into three main classes which are oil-in-water, bio-continuous and water-in-oil microemulsions. The most utilized microemulsion method is the waterin-oil for SPIONs synthesis, where the reverse micelles comprised of water-soluble droplets of reactants, enclosed by a surface-active agent monolayer created in a nonstop oil phase, which may possibly react with each other to create SPIONs. Also, SPIONs synthesis can be accomplished by either mixing two or more microemulsions that comprise of various Fe precursors and combining a precipitating agent dropwise into the microemulsion containing the Fe precursor. Within the droplets, the reactions may occur, as they primarily behave as a nanoscale reactor and the final NPs can be gathered by eliminating the unnecessary solvents or surfactants. The SPIONs’ physiochemical and magnetic properties are considerably reliant on the size of the droplet, precursors concentration and surfactant or solvent categories [15]. The oilin-water technique entails the utilization of a water-soluble form (which contains the salts of the metal, pH controllers, and covering agents), an oily phase such as hexane and surfactants acting as stabilizing agents in the interface of oil/water such as sodium dodecyl sulfate (SDS), bis(2-Ethylhexyl) sulfosuccinate (AOT) or poly(Nvinyl pyrrolidone) (PVP). The reverse microemulsion can also be accomplished and is centred on the nanosized stabilized water-soluble form dispersed in an oily phase. This process creates energetic structures that might combine and allow reaction upon blending, hence delivering a regulated nucleation growth setting. It contains a dilatory and low scalable process, which is performed at a temperature array of 20–80 °C [21].

2.3 Hydrothermal Technique The hydrothermal technique is a traditional technique utilized to produce SPIONs [28, 15]. This synthesis technique consists of a straightforward and effortlessly upscalable production technique that is based on the metal salts hydrolysis and dehydration in a water-soluble medium under elevated temperature and elevated pressure environments that are accomplished in an autoclave apparatus using a temperature of approximately 200 z C and over 2000 psi pressure. This metal oxide particle synthesis is facilitated by the reaction conditions and the ensuing MNPs precipitation. The wellregulated variables in this method include temperature, concentration, and time of autoclaving, with the latter impacting the particle size and distribution uniformity [21]. NPs are produced using this technique by accomplishing the water-soluble chemical reactions among Fe precursors in the dearth or existence of surfactants in an airtight vessel in an autoclave, which provides extraordinary temperature/vapour pressure of up to 250 °C/4 MPa for chemical reactions. At the end of the reaction, the water-soluble mixture is refrigerated down to room temperature and the

Utility of Magnetic Nanomaterials for Theranostic Nanomedicine


acquired SPIONs’ are derived from unreacted precursors, remaining surfactants, and additional impurities exclusion. By adjusting the temperature of the reaction, time of reaction, surfactant mass and precursors, the magnetic and physicochemical properties of the SPIONs can be altered using this technique [15].

2.4 Precipitation Technique The co-precipitation technique is the utmost generally utilized method, which is costefficient and a superficial production technique [13, 29]. For more than a decade, water-consistent Fe3 O4 and Fe2 O3 particles have been achieved through iron salt precipitation in water-soluble media. To guarantee their colloidal stability under physiological settings and improve their functionality, IONPs synthesized using this technique need to be covered with dendrimers, organic acids, sugars, polymers fluorescent compounds etc. This is taken on either during or after synthesis [18]. This is a widely employed hydrolytic technique for SPIONs production, where IONPs are created through precipitation between the chemical reactions of ferrous/ ferric salts of nitrates/chlorides/perchlorates/sulphates and a base (NH4 OH or NaOH) under the water-soluble condition at an insignificant preeminent temperature of 40– 80 °C. The key mechanism of reaction participating in SPIONs formations is given by Eq. 2 for Fe3 O4 . To avoid unwanted IO phase formation in the synthesized SPIONs, the reaction is generally performed in a passive atmosphere. Fe2+ + Fe3+ + 8OH−  Fe(OH)2 + 2Fe(OH)3 → Fe3 O4 ↓ +4H2 O


The following topotactic conversion paths (physical transformation to crystalline solid) are the mechanism of reaction for SPIONs formation (Fe3 O4 ), which are (1) nucleation → akaganeite phase → goethite → hematite/γ − Fe2 O3 → Fe3 O4 and (2) nucleation → ferrous hydroxide → lepidocrocite → γ − Fe2 O3 → Fe3 O4 . The topotactic conversion path is greatly reliant on the variation of the pH of the water-soluble reaction mixture and while SPIONs physicochemical properties like morphology, stability of colloidal, size and shape can be changed by variation in reaction temperature, time, reactants concentration, base type, reactant molarity and stabilizing agents [15]. A graphical illustration of the various process intended to describe uniform particle creation is shown in Fig. 5. In uniform precipitation, a quick separate nucleation burst happens when the fundamental species concentration gets to a crucial supersaturation. After that, the nuclei acquired are permitted to increase homogeneously by solute diffusion from the solution to their surface until the ultimate size is achieved. To accomplish monodispersity, these two phases must be divided, and nucleation should be prevented during growth time. The LaMer and Dinegar classical model was the first to clarify sulfur colloids formation and a restricted number of cases as seen in curve 1 of Fig. 4. But homogeneous particles have also been achieved after various nucleation procedures. Through the self-improving development process,


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Fig. 4 Development of homogeneous particles in a solution described by (curve I) single nucleation and homogeneous development by diffusion (the standard model of LaMer and Dinegar), (curve II) smaller sub-units nucleation, growth and aggregation and (curve III) numerous nucleation and ripening growth by Ostwald. [12] Adapted from Tartaj et al.; Copyright, Institute of Physics Publishing, 2003. Reprinted with permission from Institute of Physics Publishing

the homogeneity of the finishing product is attained (Ostwald ripening, curve III of Fig. 4). Also, homogeneous particles are attained due to the agglomeration effect of considerably less significant sub-units instead of constant growth by diffusion (curve II of Fig. 4). A non-natural separation between the development processes and nucleation is attained by seeding, in which external particles are launched into the monomer solution below the key super-saturation [12].

2.5 Sonochemical Technique This technique is based on the chemical reactions or metal precursors hydrolysis and condensation at low-slung temperatures, causing inorganic network creation. Monomers change into colloidal solutions to specify the sol and the evaporation of the solvent and particle introduction into the inorganic network results in the gel created [30]. This method depends on MNPs precursors hydroxylation and condensation in a solution (sol) that results in gelation at ambient temperature, and subsequent exposure to heat treatment stimulates crystalline structure creation, desired MNPs with precise size and shape [21]. This technique is built on stimulating the reaction among the blend of Fe precursors (ferric or ferrous salts) through ultra-sound treatment with frequency varying from 20–60 kHz to produce SPIONs. This ultra-sound treatment consists of varying expansive and compressive acoustic waves, which produce cavitation micro-bubbles in the Fe precursor solution, thereby induces nanocrystal nucleation by amassing the supersonic energy. Ultimately, the micro-bubbles may break down and be subject to the discharge of the stowed intense energy with a

Utility of Magnetic Nanomaterials for Theranostic Nanomedicine


Fig. 5 Graphical illustration of regularly used chemical approaches for MNPs production. [31] Adapted from Darson and Mohan; Copyright, IntechOpen, 2022. Reprinted with permission from IntechOpen from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY)


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thermal and cooling rate of greater than 1010 K/s that tends to improve the temperatures within the cavitation bubbles in an exceptionally rapid time (approximately 1 ns). Through the decomposition of water, H+ and OH− radicals are created, which further react with Fe precursor combinations to produce SPIONs. This technique is advantageous that it decreases undesirable nano-crystals growth. But this method is challenging to implement SPIONs production with controlled magnetic and physicochemical properties [15]. Through this technique, MNPs of single-phase, fine, dense, and homogeneous can be achieved. While this process is eco-friendly, it is not an exclusive technique but it shows restricted productivity and the synthesis procedure is lengthier than the co-precipitation technique [30]. Figure 5 shows the graphical illustration of regularly used chemical procedures for MNPs’ production.

3 TRC Utilization of MNPs In certainty, MNPs show, not just individual distinctive materials properties but also a combined strategy capacity for targeting cells, treatment, and imaging, which make them perfect platform materials for TCs [4, 5]. The word “TCs” represents a broad set of physical theories, nanotechnological techniques and biomedical and engineering processes which provide different prospects for diagnostics and treatment and utilize as a rule similar hybrid NPs. The following possibilities are offered, which are 1. Timely diagnostics and pharma-cogenomics 2. Three and four-dimensional (3-D or 4-D) tomography of the object in doubt, employing a molecular-level resolution (superior-resolution real-time imaging). 3. Evaluation of the disease’s progression phases, treatment plan development and restorative technique choice, which is targeted at the molecular stage and customized. 4. Directed transport of diagnostic and TRC agents, its regulated delivery from nanocarriers and regulated activity, while actions are taken to protect and safeguard the degrading of the active substance during its transportation via the body and the organism from substance noxious influence. 5. Treatment examination and modification and the examination of the status of the patient after completing effective therapy. 6. Assessing the substances’ biocompatibility and the processes for remote control, their noxiousness, possible dangers, and vulnerabilities The various major TC methods developed thus far, differ in the chemical and physical effect types utilized (X-ray, radioactive, radio-frequency (RF), electromagnetic, biochemical ultrasonic and their blend) [9]. Personalised targeted TC nmed has been developed as a key method for improving the sensitivity and specificity during identification in addition to the probability of existence by utilizing NPs. A potential NPs that are the most beneficial tool for the detection, identification and therapy of tumour is the TC NPs. To prevent the unrestrained tumour cells spread, nanosystems have been designed and in practice,

Utility of Magnetic Nanomaterials for Theranostic Nanomedicine


systems made from MNPs including anticancer medicine have shown an advanced healing index when compared to conventional chemotherapy, thereby resulting in a substantial decrease in the noxiousness of the nanosystem [32]. They tend to amass at the target site in the presence of MF, which is of enormous importance in TC applications. The magnetic moment of IONPs should be elevated and allow for their exact bonding to biomolecules of interest. They should also have the capacity to resist different biological and physical conditions [13]. Nevertheless, despite the extensive progress and technological advancement, there are particular inherent shortcomings which set limits to their medical application, which is that they lack exclusiveness, localization, and temporal and spatial resolutions. They also offer just imperfect control over drug release and activity. The risk of side impacts is relatively high, and the techniques are difficult to execute, and high-priced paraphernalia and assets are required [9]. A critical part is played by personalized treatment methods employing nmed, which is useful for disease therapy with changing representations among persons and blocks patients’ unpredictability in medicinal responses. This is ascribed to the distinctive physical, biological, and chemical properties of NMs in comparison to their molecular and bulk equivalents. They also have added advantages in nmed such that they can be remotely sensed and controlled using an external MF (EMF) [33]. Owing to these benefits, they have been exploited successfully for a wide array of biomedical purposes. MNPs’ distinctive properties like their sensitivity and precise registration for diagnostics are allowed owing to living tissues practically lacking ferromagnetic materials and zero signal strength weakening of the MF from biological tissue (contrasting optical and electrical methods) [8, 34]. In MNPs imaging approaches, these properties are utilized to precisely determine the location and concentration of particles like magnetic susceptibility imaging (MSI), magnetic particle imaging (MPI), and magneto relaxometry imaging (MRI). Also due to MNPs’ miniature size, they can effortlessly intermingle with viruses, cells, genes, and effectively enter all sections of the human body. They are also extremely tuneable and by altering their size and process composition or synthesis, their behaviour and preferred physical properties can be achieved (slow/fast exclusion from the human body and their particular response to MF applied). Finetuning these particles by coating them with certain molecules facilitates their binding to certain entities and thereby allows molecular imaging [8]. In MNPs’ biomedical use, they are categorized according to their usage in the core (in-vivo) or outside (in-vitro) of the human body. In-vivo functions are extra divided into TRC (HT) and delivery of drugs and diagnostic (nuclear magnetic resonance imaging (NMR)) applications. While the in-vitro procedure is employed just in diagnostic (separation or selection and magnetorelaxometry) [9]. For in-vivo use, NPs that are magnetically sensitive are fabricated by employing any of the biological or chemical procedures. While the physical technique is primarily employed for the production of MNPs used for in-vitro purposes. MNPs carrying inorganic or natural surface coverings have accomplished growing importance in the material science sector owing to the ensuing instruments allowing a well-regulated sensory system


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for advanced bio-medical usage from medicinal and diagnostic to bio-separation [13]. In planning an effective nano-platform-based TRCs, these four critical attributes need to be taken into account, which is choosing a potential TRC, varying from tiny molecule drugs to bigger peptide or nucleic acid, a steady carrier, adopting an aiming and drug delivery approach and prudently singling out an imaging agent [35]. Owing to their magnetic properties, MNPs have been applied generally as CAs in the screening of tumours employing MRI, computed tomography (CT), near-infra-red imaging (NIR) and magneto-acoustic tomography (MAT). They are also utilized in the therapy of tumours via PDT, PTT and MHT. All these different approaches are employed in oncology, but the most excellent medical impact is generally guaranteed through the blend of strategies as the integrated model allows MNPs to achieve several tasks concurrently [36].

3.1 MHT MHT is a positive non-intrusive method for the treatment of cancer [37, 38]. The word HT is derived from two Greek phrases “hyper” and “therme” connotating “rise” combined with “heat” in that order, owing to the condition attributing it to improving body temperature. HT has been widely considered by employing biocompatible MNPs as heat facilitators for the treatment of tumours owing to the elevated effectiveness and a particular level of side impacts. It is a pioneering and novel heat treatment where MNPs are the heating-generating agents [39, 13]. HT is one of the tumour therapies among radiation treatment, chemotherapy, surgery, gene, and immune treatment. It is thought of as a synthetic approach for improving the temperature of the body cell by supplying heat taken from peripheral sources to prevent or destroy the further growth of malignant tissues [39]. The generated heat from MNPs in a non-disturbing AMF to the cancer cells causes cell fatality through irreversible physiological variations is identified as HT as depicted in Fig. 6 [13, 40]. HT refers to a body temperature increase by 1 ◦ C. It also refers to the temperature array rise to 39–45 ◦ C. The four kinds of HT include fever, movement-associated HT, deficient temperature drainage HT and medication-induced HT. For wholesome human somatic cells excluding neurones, they can endure at a temperature of 44 ◦ C for a minimum of one hour. Hence, wholesome tissues are not harmed by HT except if the temperature exceeds the stated value above [41, 42]. For a temperature array of 45–50 ◦ C, HT causes thermal extirpation. Though it can be unsafe for an organism, it can be of medical purpose, particularly when focused against certain tissues or cells. TRC HT is grouped by matching the size of the area where the temperature is increased, and it is grouped into whole-body and local regional HT. In constrained body areas, temperature increase permits for the determined TRC impacts on the suitable sections of the body while reducing adverse impacts of heating in other body areas. One of the viable therapeutic techniques for increasing temperature in

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Fig. 6 Principle of HT. Through the application of AMF, MNPs are aimed at tumour cells. Subsequently, the heat produced by the MNPs produces constricted heating of the tumour cells with a temperature range of 41–47 ◦ C. CITATIONKhi21\l7177; Adapted from Khizar et al. Copyright, ACS Publications, 2021. Reprinted with permission from ACS Publications

a particular body section is MHT [41]. The concept of employing SPIONs for HT was first proposed in the 1950s by Gilchrist et al., and its original biological system application was performed in 1979, with various MNPs types having been studied for this objective since then [17, 37, 43]. With the upswing in NT, MNPs introduction has further advanced this method into a well-studied field. The extremely important benefit of MNPs’ mediated MHT remedial mode is in the intense tissue permeation and mag-selectivity cancer cells obliterating devoid of impairing the wholesome tissues. This technique assists in understanding intracellular HT, as it precisely provides medicinal heating to the tumour cells, and this intra-cellular HT can be more developed by the cell-targeting ligands conjugation with MNPs’. The local and uniform heat leads to better selectivity and therapy efficiency. Owing to the benefits of these TRC methods, MNPsMH-based benign tumour therapy has lately been transformed from the research laboratory to medical tests and they have been utilized for glioblastoma and prostate cancer (PC) therapy [44]. MHT involves the conversion of electromagnetic energy from external AMF into heat employing MNPs and the MNPs act as the nano heat centres creating heat by relaxation loss, thus heating the tissue. The key objective of efficient treatment of cancer is the destruction of cancerous cells with minimum harm to cells that are normal. This technique can be utilized for selective heating of a miniature region, as it presents the capability of being an extremely discerning and non-intrusive method for TRC cancer therapy [17]. About MNPs in TRC applications, MHT is deemed the utmost capable treatment for cancer therapy. In MHT, a superficially utilized alternating MF (AMF) is applied to the MNPs’ thereby heating up the MNPs and enhancing the temperature of their


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environments. With the implant of particles in a tissue tumour, the local heating of the tumours is permitted without damaging wholesome cells. Precise delivery of the medicinal agents such as drugs, genes, radionuclides etc. attached to the particles at the desired location is possible with the internal or external application of applied stimuli like osmolarity, temperature, pH, and MF intensity (MFI). This delivery of the local drug permits the reduction of the overall dispensed dosage resulting in to a lesser extent general side effects [8]. MHT treatment is a confined thermal treatment utilized for cancer/cancerous tumour therapy in which SPIONs perform as heating-producing agents. SPIONs are usually delivered and confined near a tumour location through active/passive/ magnetic targeting and consequent exposure to an AMF for approximately 1–2 h specific time. The heat produced by the process increases the tumour temperature to approximately 42–45 °C and is employed in cancer cell therapy. The heat-induced terminates various cellular functions as well as the propagation of cells and gene representations in tumour cells which inclines to cause the death of cells through programmed cell death. The heat generated during this treatment produces a very negligible impairment to the adjacent typical cells/organs as associated with other traditional therapy techniques [15]. Due to this, the temperature in the interior of the benign tumour is enhanced owing to the single-domain particle’s energy dissipation triggered by the Neel fluctuations of the NPs magnetic moment and peripheral Brownian fluctuations. The value of heat dissipation changes with the amplitude and frequency of the AMF and the magnetic properties of NPs. Tumour cells are destroyed with enhanced temperature due to folding, denaturation, apoptosis, protein aggregations, necrosis and coagulation and unintended response which is facilitated by the immune system activation supported by over-expression of heat shock protein. Also, the heat created through this technique can be regulated by adjusting the SPIONs’ magnetic/physicochemical properties such as the shape, size, Ms, dispersion medium, applied AMF and surfactants [15, 37]. HT can be induced in SPIONs via the exchange by suppression of anisotropy wall by the MF, Brownian spin, thermal activation and the combination of the preceding factors [45]. The two mechanisms accountable for the creation of heat from MNPs are hysteresis losses and the Brownian Neel relaxation (BNR). The BNR generally happens in SPIONs and it entails the quick spin of the magnetic moment within the domain in the instance of NR and in the instance of BR, it involves the physical spin of NPs within the fluid in the peripheral AMF presence. The subsequent equations give the Brownian (τ B ) and Neel (τ N ) relaxation times which sturdy changes with the NPs hydrodynamic size of nanoparticle and extremely changes with the fluid viscosity and the effective relaxation time (τ ) (Eqs. 3–5). τB

3ηVH kT

τ N = τ O ex p


(3) (4)

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τB τN τB + τN



τ0 , K, VM , k, T, ï, and VH represent the distinctive flipping frequency, the magnetic anisotropy constant, the volume of NPs, the Boltzmann constant, the temperature, the fluid viscosity, and the NPs hydrodynamic volume, respectively. The dissipation of heat from MNPs is due to the delay in the magnetic moment relaxation under the peripheric AMF application with a time delay, which needs a magnetic reversal lower than the NPs’ relaxation times. The dissipation of heat (P) changes with the frequency (f), the AMF amplitude and the NPs’ magnetic properties (Eq. 6). P = μO χ f H 2


μ0 , χ , and H signify the permeability of free space, the magnetic susceptibility, and the AMF strength, respectively [37]. In guiding NPs to tumours, further, improvement has been made by employing targeting agents like antibodies for this purpose. This technique is appropriate for efficient cancer treatment if particles concentrations in the benign tumour are extremely adequate and substantially greater in the surrounding regular tissue and a high enough specific absorption rate is possessed by the particle which is given by the specific heat absorption rate (SAR) in Watts per gram (Eq. 7). SAR =

cT t


c and T represent the precise heat capacity and increase in temperature in the interval of time (t) to transport substantial intra-tumoral amounts of heat with AMF that is highly allowed by the ordinary cells. The values of SAR change with the NPs’ shape, size, and magnetic properties as well as the amplitude and frequency of AMF, the attributes of the materials employed for coating and the functionalization of the material surface [37, 43, 46]. The various NPs heating tools explored for TRC purposes are optical heating employing laser, small bubbles heating employing ultrasound and IO heating owing to AMF which involves the use of physical processes known as hysteresis heating. Optical techniques efficiently heat particles but are relentlessly constrained by laser light reduction by the cells. While ultrasound heating is encouraging, due to energy being focussed on a certain spot, it nevertheless deteriorates from the change of sound speed in most cells and in various applications, from the narrow applicator aperture. To achieve therapy of cells positioned practically wherever in the human body at crucial depths is achievable by applying magnetic particle heating. Particles utilized for heating may also be appropriate for medical imaging purposes also [43]. There is selective or entire body heating in specific regions in various ways. For high temperatures utilization, there are three vital medical methods used, which are whole body HT (WBHT-employed for the treatment of metastases over the entire body), regional HT (RHT- body parts like the limb, organ, or body hole are heated)


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and local HT (LHT-superficial local and interstitial local HT) [37, 39]. Tumours are heated with microwave energies of wavelengths varying from 433 to 2450 MHz, radio frequency varying from 100 kHz to 150 MHz, ultrasound, perfusion of hot water (blankets, tubes), NPs ferromagnetic seeds, resistive wire implants and infrared radiators. WBHT is often employed in childhood refractory malicious solid cancers to enhance cancer sensitivity to chemotherapy and its impacts. While LHT is employed for heating a small-scale area comparable to cancer of ≤3–5–6 cm in the lengthiest thickness. In the RHT, it is normally blended with radiation treatment or chemotreatment, and it is most time dedicated to developed cancer located in the abdomen treatment such as prostate, cervical, bladder, colorectal and ovarian carcinomas, main and lower pelvis or thighs (soft cell sarcomas) [39]. In the study by Bhardwaj et al. [47], self-adaptable temperature-manipulated NPs were synthesized (Mn-Zn Ferrite NPs) and their impact on the killing of cervical and breast tumours was considered. Testing the synthesized MNPs on the tumours, it was reported that various sessions of HT on the tumour cells utilizing a 24–72 h window using trypan blue assay of at least 3 shifts of 1 h were needed for the overall elimination of the tumour cells, with cell viability decreasing to 25%, 15.8% and 0% owing to HT sessions employing MF, MF alone and MF along with three HT sessions after 72 h are indicated by Fig. 7. Magnetoliposomes (ML), which comprised of SPIONs stabilized by phospholipid-bilayer exposed to AMF of 40–47 kAm amplitude and 270 kHz frequency to produce heat, were explored for HT impact on human Pancreatic ductal adenocarcinoma (PDAC) cells (Mia PaCa-2 and PANC-1). The impact of MHT on the viability of the cell of the organoid cultures and the cell lines was explored at two diverse time points. No cytotoxic impacts at 300 and 225 μg(Fe)/mL ML concentrations were shown by the cells of Mia PaCa-2 and PANC-1 and PDAC organoid cultures. MHT therapy had the uppermost effect on the viability of cells using ML, which resulted in outstanding cell viabilities of 2 and 24 h post-therapy [48]. While in the study by Parekh et al. [49], the co-precipitation procedure was employed to produce auto-tunable temperature-sensitive IONPs of the size of 11.3 ± 0.2 nm and utilized for MHT to determine the cytotoxicity of cervical tumour cell line HeLa under MF induction heating of 350 kHz frequency and field of 14.2 kA/m and without MF induction heating. Cell death of approximately 75% was noticed for the cytotoxicity assay after the utilization of MF induction heating for 24 h of the cell interface with the magnetic fluid, with just about total death of tumour cells observed with interaction time increased to 36 h and HT heating session of 1 h (Fig. 8). Particle-size precise SPIONs of γ − Fe2 O3 and Fe3 O4 were prepared through the hydrothermal technique and were improved with whey protein isolate (WPI) to create spherical/diamond-shaped structures of bio-altered SPIONs with a diameter range of 20–100 nm. To carry out HT experiments, SPIONs loaded with adriamycin (ADM) were utilized in vitro and in vivo test of HepG2 cell inhibition in the skin of mice placed at the centre of an AC electromagnetic coil with MF of parameters of frequency (f) of 100 kHz, field (H) of 169 Oe (13.62 kA/m) and H.f of 1.36 × 109 A/ms. It was noticed that the size of the HepG2 cancer cells was decreased with the consistent surface consumed and gelled thereby causing the cancer cells to lose

Utility of Magnetic Nanomaterials for Theranostic Nanomedicine


Fig. 7 Various HT sessions of 0.35 mg/mL MF concentration a HeLa cells viability employing Trypan blue assay after 24–72 h therapy b1–b4 HeLa cells morphology after 24 h, c1–c3 after 48 h and d1–d3 after 72 h. [47] Adapted from Bhardwaj et al.; Copyright, Springer Nature, 2020. Reprinted with permission from Springer Nature from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY)

their biological movement when the cells were treated in vitro and in vivo using WPI-altered SPIONs for HT therapy [50]. While the chemical co-precipitation and thermal decomposition techniques were used to produce SPIONs-based ferrofluids, which were functionalized with carboxyl (terephthalic acid-TA) and used to study the heating efficiencies of TA@SPIONs on in vitro MHT therapy of MCF-7 breast


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Fig. 8 Viability of cell employing magnetic fluid in the presence and absence of MF induction heating after 24 h at 350 kHz frequency and 14.2 kA/m applied field. [49] Adapted from Parekh et al.; Copyright, Elsevier, 2020. Reprinted with permission from Elsevier from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY)

tumour cells. An outstanding time–temperature increase was noticed employing the water-soluble ferrofluids under the applied AMF and this resulted in elevated SAR varying from 23.4 to 160.7 W/gFe owing to improved magnetic response through π -conjugations of TA molecules short-chained on the SPIONs. It was reported that TA@SPIONs-based fluids of 1 mg/ml concentration in MCF-7 tumour cells, whose temperature was kept at 45 °C under the exposure of AMF for 1 h, demonstrated stimulated substantial mortality of cells [51].

3.2 MRI MRI is a non-intrusive TRC diagnostic tool that examines the variation in the hydrogen protons in water molecules magnetization enclosed in tissue when positioned in an MF and subjected to a radio frequency electromagnetic wave pulse [17]. MRI are diagnosis method in radiology that utilize magnetism, computer expertise and radio waves theories to create structural human body images. An efficient way to identify the cancerous tumours positioned hidden within the body is the utilization of NPs-based CAs for MRI [15]. MRI is intensely utilized for the screening of cancer throughout and after chemotherapy. In spite of the common imaging methods which need ionization radiation, MRI employs ion magnetic properties for image prediction. With no application of magnetic moment, there is a randomized location of the protons and there is a corresponding or antiparallel alignment of protons when the MF is applied. To improve the image quality of MRI, CAs like those based on MNPs are utilized. The advancement of sensitive MNPs and colloidal magnetic particles for biomolecules control and simple magnetic separation is of excellent significance for initial disease discovery and therefore in treatment administration and the initial phase of tumour therapy. Discerning tumour cell detection can be accomplished by

Utility of Magnetic Nanomaterials for Theranostic Nanomedicine


antibodies, hence various immune sensors have been created for this application. While the use of MNPs functionalized with antibodies specialized for a variety of cancer cells, the exposure via the certain immune sensor can be linked with imaging via MRI and the therapy of cancer via HT. This approach presents a considerably enhanced rate of persistence among oncologic patients’ treatment responses [36]. MNPs are generally employed for diagnosis and efficient delivery of drugs owing to the ease of their imaging by MRI. Nevertheless, MRI is an efficient technique for imaging tissues hidden inside the human body with high resolution, there is a necessity for peripheral agents that can improve the contrast to show objects distinctly. To improve the contrast by enhancing the photon relaxation time, various metallic NPs such as Gd, manganese (Mn) and SPIONs are utilized. Gd-based CAs for MRI are now Food and Drug Administration (FDA) authorized. But IONPs are generally used owing to their excellent magnetic properties, huge surface area to volume proportion and their capability to deliver drugs which makes them appropriate for nano-TCs [52]. IONPs were first employed as a T2 -MRI contrast agent (CA) and several novel magnetic modifications have been created to enhance the sensitivity of the signal for improved MRI diagnosis. Also, these NPs platforms can adapt other corresponding imaging sensory systems, medicinal drugs and aiming ligands and attain extremely precise imaging and efficient restorative purpose. Furthermore, their platforms can act as magnetic switches for the control of the molecular level of cell functions and signalling [4]. In the recognition and planning of cancer therapy, an important instrument utilized is MRI. But a specific imaging method is not suitable enough to assess various attributes of cancers owing to the sensitivity, resolution and specificity of detection drawbacks. In cancer therapy, the exact distinction between tissues that are cancerous from tissues that are healthy should be carried out during diagnosis to sidestep serious harm to regular/nearby tissues and have efficient therapy. This is achievable by employing multi-modal diagnostic methods like MRI as an accessory to fluorescence imaging, to improve the spatial resolution and detection sensitivity in the imaging of cells. This is achieved by creating a multi-functional NPs system through the coupling SPIONs (MRI) along with other fluorescence agents such as quantum dots (QDs) and fluorescence dyes such as carbon QDs, and fluorophores [15]. The generally utilized MRI CAs in medical treatments are centred on Gd complexes (Gd(III)) including OptiMARK (Gadoversetamide, Gd-DTPA-BMEA), Omniscan (Gadodiamide, Gd-DTPA-BMA), Magnevist (Gadopentetic acid, GdDTPA), and Multihance (Gadobenate disodium, Gd-BOPTA) are employed as constructive CAs. However, great fears about Gd-based complexes and nephrotoxicity possible well-being threats have been raised by different research studies. Hence, getting a substitute for Gd-based CAs for MRI imaging is critical. Lately, SPIONs were introduced as a negative MRI CA (FDA approved) owing to these NPs inclining to unwind in a crosswise direction and being green/biocompatible and dependable in comparison to the complexes of Gd [15].


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Typical imaging employing MRI is founded on proton density (PD), longitudinal (T1 ) and transverse relaxation (T2 ) classifications [53]. T1 is known as the rotation lattice relaxation time, which correlates to exactly how swiftly the magnetization that is corresponding to the fixed MF improves after a perturbation is used on the system. While T2 correlates to how swift the magnetization in the plane at right angles to the unchanging MF loses coherence. The processes of transverse and longitudinal relaxation are separately and concurrently executed. Though T2 is generally far from the point (shorter) of T1 , this variation allows for the distinguishing of tissues [54]. The magnetization mapping gives an organ image, with protons in various tissues with variable water concentrations reacting inversely. To improve the images, CAs are utilized, and they impact the proton’s performance in their locality leading to clearer images. In MRI, CAs employed are T1 and T2 CAs which are based on their impact on the proton MX activities. The most popular T1 CAs utilized are paramagnetic compounds consisting of metal ions (MI) Gd3+ or Mn2+ and chelating ligands like diethylene triamine penta-acetic acid (DTPA). The chelate stops MI from binding to chelates in the body making the paramagnetic ion less noxious. T1 CAs largely decrease the longitudinal relaxation time, which is because of the exchange of energy between the spin and surrounding lattice (spin–lattice relaxation) and will cause a sharper indication. While T2 CAs, comprising of SPIONs like Fe3 O4 have a sturdy impact on the transverse relaxation time. In EMF, NPs are magnetized, and induced MF locally is created. These induced fields agitate the MX processes of protons in water molecules reducing the T2 relaxation time, resulting in MR images blackening [17]. The application of MNPs in diagnostic is achieved in MRI and this method is based on the variation in the nuclear MXs of the protons of water in biological media and around sturdy tissues. The nuclear MX rate of its surrounding protons is changed by the CA and the signal contrast is modified. Its contrast improvement effect is determined by the relaxation rate (R = T1 (s −1 )) and the relaxivity (r = R/concentration (mM−1 * s−1 ). A better contrast impact is associated with a higher relaxivity [16]. Also, MRI through SPIONs in a real-time setting can be accomplished for instantaneous routing, localization, and drugs are released at the sites of a tumour to track their bioavailability. While combined targeting consists of magnetic and active targeting methods and a conventional combined drug delivery method may comprise of SPIONs, chemotherapeutic/anticancer drugs, moieties targeting and/or carrier [15]. With regards to MRI, the key focus in recent studies has been the creation of MNPs specifically SPIONs for the improvement of contrast in unhealthy tissue [55]. Biocompatible IONPs payloads coupled with a prostate-specific membrane antigen (PSMA)-aiming antibody, J591, through 1,2-distearoyl-sn-glycero-3phosphoethanolamine-N-[amino(polyethylene glycol) (PEG-DSPE) linkage to improve MRI in orthotopic prostate tumour (PT) bearing NOD/SCID mice for 2 and 24 h after intravenous inoculation of J591-MNPs was explored in this study. The tumour cell viability was not impacted by the MNPs in vitro and antibody specificity and improved cellular Fe uptake were not compromised by their coupling to J951. The contrast of the cancer cells was amplified in vivo by employing PSMA-targeting

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MNPs, hence having the potential to improve MR recognition and localization of PTs [56]. Ferrimagnetic H-ferritin (M-HFn) NPs created were employed for in vitro MRI and immunohistochemical staining of MDA-MB-231 breast tumour cell application, performed at 7 T and gestated for 24 h. It was noted that the relaxivity, magnetic properties and peroxidase-like activity of the created NPs were size reliant and substantially improved the MRI and cancer cell staining implementation owing to the huge core magnetite core in the NPs as depicted in Fig. 9 [57]. MNPs synthesized via the precipitation method and coated with poly-L-lysine (PLLMNPs) to enhance their biocompatibility and stability were utilized for the joint MHT and MRI appropriateness by calorimetric and parametric mapping extent for cancer cells. It was reported based on the approximate heating rates, that the SAR values of the PLLMNPs were approximately 14–15 W/g at 190 kHz frequency and AMF of 8kA/m. While the significant impact of the PLLMNPs on the transversal relaxation time (T2 ) with the relaxivity (r2 ) which was approximately 487.94 m/Ms was reported for the MRI parametric mapping measurements. These results showed the prospective efficiency of the NPs as a negative CA for MRI use in BMD [58]. In the study by Wu et al. [59], Fe3 O4 was prepared and activated with carbodiimide and cross-connected with α-ketoglutarate chitosan (KCTS). The surface of the prepared MNPs was combined with antibodies of lymphatic vessel endothelial hyaluronan

Fig. 9 Schematics of immunohistochemical staining breast tumour cells by the gestation with NPs a without the gestation of the NPs, gestation b with M-HFn1000, c M-HFn3000 , d M-HFn5000 , and e M-HFn7000 Fe atoms loading and f various density mean showing the section of tissue therapy using the NPs of huge core sizes which improved immunohistochemical staining efficiency. [57] Adapted from Cai et al.; Copyright, Dovepress, 2015. Reprinted with permission from Dovepress from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY)


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receptor 1 (LYVE-1) and Podoplanin and employed as a dual targeting magnetic nanoprobes to determine the lymphatic endothelial cells (LECs) in cancer metastasis. As observed in Fig. 10a, the in vivo image of the cancer cells showed no fluorescence before the synthesized KCTS-LECs@Fe3 O4 dual antibody was injected into NOD/ SCID mice and while there was improved fluorescence reaching the peak of 12 h from the cancer cells with the inoculation of the KCTS-LECs@Fe3 O4 dual antibody. Also, there was a steady decline in cancer cell imaging, reaching its lowest phase after 12 h and resulting in continuous improvement with time (Fig. 10b). While in the study by Zhu et al. [60], SPIONs coupled with PSMA targeting polypeptide were created as a CA, employed in vivo and assessed in LnCaP PTbearing mice using the MRI method. Precise uptake of the created polypeptideSPIONs (PPE@SPIONs) by PSMA-expressing cells was reported in vitro. The signal of MRI imaging was reported to be exclusively improved in PSMA-expressing cancer cells with the established PPE@SPIONs and additionally, diverse accretion of SPIONs in the cancer tissues was also noticed from the Prussian blue staining.

Fig. 10 Representations of the imaging through fluorescence and MRI colorectal tumour intravenous xenografting cancer models of NOD/SCID mice a no intravenous injection of the KCTSLECs@Fe3 O4 to the cancer cells in sedated NOD/SCID mice and fluorescence imaging at preinjection and post-injection at 0.5–24 h and intravenous injection of the KCTS-LECs@Fe3 O4 to the cancer cells sedated NOD/SCID mice and imaged using 3 T MRI image scanner at pre-injection and post-injection at 0.5–24 h. [59] Adapted from Wu et al.; Copyright, Springer Nature, 2015. Reprinted with permission from Springer Nature from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY)

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4 Optical Intrusion Techniques Employing MNPs for Cancer Treatment The two therapy techniques associated with optical intrusion are PDT and PTT The two emerging tumour therapy techniques with huge potential are PTT and PDT, with resources being utilized in these methods under rigorous study. Almost all NMs employed in these techniques are due to their distinctive fluorescence properties [61]. These emerging techniques in cancer treatment using MNPs are further discussed in the following sections.

4.1 PTT Thermal treatment (HT) has progressively advanced in the treatment of tumours owing to the leading impact of tissue extirpation for a prolonged period. Bear in mind that aiming HT at certain cancer sites can efficiently impede unwarranted harm to regular tissues, hence PTT has become an exceptional therapy preference. In this technique, vibrational energy via PT properties of MNPs is released and converted into TE, thereby leading to the killing of cancerous cells [62]. In cancer treatment, a decent substitute to utilize as photothermal (PTT) agents is MNPs. Such NPs are employed in a mixture with other materials or employed as PTT agents and the mixture of MNPs with other photothermal agents inserts extra capacities into the TRC system. Along with the MNPs with two-fold magnetism and near-infrared (NIR) absorption functions, IONPs stand out as appropriate NPs for PTT. PTT have an excellent prospective for biomedical usage as it can be guided magnetically to the location of concern and their dissemination in cancer cells and other organs imaged. AMF blending with IR absorption into a specific composite makes it feasible for NPs to be steered to the cancer cells. They also can be employed to visualize cancer location via MRI or thermal imaging for true-time therapy monitoring thereby increasing the effectiveness of the heating [13]. PTT denotes the utilization of desirable agents such as infrared wavelength and materials. Direct local and systemic delivery are the conventional techniques for distributing MNPs to tumour tissues. In MNPs, direct local delivery is probable when the tumour position and degree are recognized and effortlessly available for delivery, which is generally via an injection. While in systemic MNPs delivery, designed MNPs are injected into the blood flow and extensive circulation leads to the accumulation of extremely vascularized tumour tissues [39]. In this technique, materials having outstanding PT conversion effectiveness are utilized to enhance the targeted tumourous region temperature, thereby leading to the death of the tumour cells [61]. Employing this technique involves unhealthy tissue irradiation with electromagnetic radiation using the VIS–NIR light to cause thermal impairment to tumour tissues [1, 63]. In this technique, laser energy is sorbed by the photo-absorbers and


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transformed into heat. They can cause genetic alterations extending from the structural changes in protein to tissue carbonization. The increase in temperature using this method ranges between 45–300 °C and the medicinal impacts can be gotten at sufficient depths by employing the NIR irradiation. Their three-dimensional specificity and negligible intrusiveness make this technique an attractive medicinal sensory system in comparison to other intrusive medical techniques. To treat tissues, continuous wave or pulsed lasers are used in PTT. In the pulse laser utilization in PTT, extreme heat is made as the width of the pulse laser employed is briefer than the tissue thermal relaxation time (usually > 100 W). While in the continuous wave laser utilization in PTT, adequate laser energy is required to be accumulated in the target region prior to loss of heat in the tissue owing to blood perfusion. To get a useful thermal medicinal response, the laser parameters should be selected correctly and the radiance of the laser needs to be selected at a wavelength where the unhealthy tissue has an above-average absorbance than the neighbouring tissues [1]. The effectiveness of PTT in tumour research is generally studied using in vivo, in vitro and in-human medical assessments. In the in vitro PTT, it involves the main stage in NMs assessment as a prospective PT agent in the organic environment, where NPs are transfected to the cancerous cells and simmered at 37 ◦ C for a specific amount of time using laser light to illuminate the NPs coopted by the cell and leading to the death of cells resulting from the heat generated by the NPs. The impact of in vivo PT depends generally on the NPs, concentrations in the cancer cells and the NPs are inoculated into mice via intratumorally or intravenously. Factors that impact the incorporation of NPs into cancerous cells and subsequent treatment using laser light are the inoculation time, their shape, size and surface chemistry [64, 65]. When the power of the laser is minimum, the exposure time of the laser is extended. The other way around is the effect of the power of the laser when it is above average, the time of exposure to tissue is decreased. The various classes of lasers employed for PTT treatment differ from each other by the length of adsorption and wavelength. The near-infrared laser (NIR) is generally employed in PTT owing to its 1000 nm profound penetration impacts and can be employed in the continuous and pulse modes. The death of cells as a function of the laser and temperature exposure time is given by the Arrhenius rate analysis [64]. In this segment, the detailed use of various MNPs for the PTT of cancer cells from prior research will be reviewed. An in vitro chemo-treatment and PTT of hepatocellular carcinoma (HCC) employing polydopamine (PDA) covered Fe3 O4 NPs and the functionalization of spheres (sMAG) with a derivative of folic acid (FA). It was reported that NMs bearing the FA targeting moiety were effective in the destruction of the tumour cells (HCC) using the dual techniques, with the magnetic sphere showing more effectiveness in this sensory system and elevated PTT response [66]. Synthesized MNPs coated with carbon (C@MNPs) were employed for PTT through the irradiation of human PC3 cells (human fibroblast sarcoma (HT1080) cells with a NIR laser beam. Death of cells in C@MNPs and laser beam presence was confirmed by the changes in the morphology and the propidium iodide fluorescence enclosure analyse [67]. While fabricated C@Fe3 04 NPs were assessed for PTT to destroy human lung adenocarcinoma A549 cells employing in vivo NIR treatment. It was reported that 98% of

Utility of Magnetic Nanomaterials for Theranostic Nanomedicine


cells were eradicated in 10 min of using 808 nm NIR laser treatment (2.3 W/cm2 ) on the NPs to generate rapid heat. The NPs provided a superior PTT impact through intratumoral delivery and NIR radiation of the cancer xenografts. Figure 11a depicts mice images after the administration of the fabricated NPs, which were illuminated with NIR laser light. It was reported that the size of the cancer was significantly decreased and the temperature out of the cancer tissue xenograft increased to 49.4 ± 3.9 °C within 10 min with the application of NIR laser light (Fig. 11b). While in Fig. 12c, the size of cancer cells removed from the mice was reduced significantly when compared to before the treatment using NIR [68]. The coprecipitation technique was employed in this study to fabricate MNPs, which were subsequently employed in vitro and in vivo PTT of A549 cancer cells by the application of NIR treatment at 808 nm. With the irradiation of the cells using NIR, clusters of the NPs were noticed to induce elevated heat on the cells, which showed more cytotoxic against the cancer cells than the specific NPs. A statistically substantial reduction in the growth of the tumour in mice which was treated with the NPs and irradiated with NIR laser light was noticed, with cancer size decreasing from 955.3 mm3 in controls to 222.8 mm3 at 19 days [69].

Fig. 11 Intratumoral administration of the NPs using the in vivo NIR treatment a cancer size variations of the mice’s entire body (upper images) and removed cancer mass, b change in temperature on the cancer xenograft after NIR treatment and c cancer size variations. [68] Adapted from Lee et al.; Copyright, Dovepress, 2015. Reprinted with permission from Dovepress publishers from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY)


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Fig. 12 a Cytotoxic and b photo-toxicity of Fe3 O4 -Ce6-FA NPs in MCF-7 and PC-3 cell lines. [74] Adapted from Choi et al.; Copyright, MDPI publishers, 2018. Reprinted with permission from MDPI publishers from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY)

4.2 PDT PDT is an emerging, superficially activatable therapy sense modality for different disorders. PDT is a clinically authorized therapy for various ailments including tumours and presents various benefits over traditional chemo-treatment by offering extra selectivity via the three-dimensional light confinement utilized for the stimulation of the photo-sensitizer (PS). It involves the non-noxious drug or dye known as PS administration to a patient bearing a lesion which is frequent but not always a tumour through a general, local or contemporary process. After the appropriate maturation period with the PS, there is selective illumination of the lesion with the light of proper wavelength and the oxygen presence leads to cytotoxic species creation and subsequent destruction of tissue and death of cells [1]. PDT is a superficially stimulated and marginally intrusive sensory system for the treatment of cancer [70]. It comprises of the general utilization of photo-inducing drugs (photo-inducer), which are photoexcited in the tissue employing suitable light wavelength and power. The excitation of these photo-sensitizers (PCs) is the presence of oxygen, hence the delocalization of electrons from the ground to the excited states. This phase is trailed by light activation of a suitable wavelength, with the transport of an electron to the neighbouring tissue and thereby leading to the production of oxygen free radicals (reactive oxygen species-ROS) which triggers tumour or cancer cell destruction. To improve the PCs’ impacts, the strategy of MNPs as targeted drug delivery procedures has to turn out to be of attention [36]. In the PDT, a PC is amassed in tumourous locations, and a specific wavelength of light is employed to irradiate the location of the tumour cells leading to the generation of singlet O (O2 ) and further cytotoxic reactive O causing necrosis or apoptosis [61]. PDT is generally partitioned into anti-microbial PDT (AMPDT), cancer-targeted PDT (CTPDT), and vascular targeted PDT (VTPDT). Most PDT is centred on the cellular-aimed photo-chemo treatment [71].

Utility of Magnetic Nanomaterials for Theranostic Nanomedicine


With a whole array of photo-sensitize assessed so far, just not many have been productively moved from bench to bedside use. In tumour treatment utilization, PDT is most desirable owing to its important selectivity and specificity. This is due to the exclusive concentration of PC within the cancerous tissue, with the direct focus of light on the lesion, causing PDT ROS to be created ensuing in the cellular obliteration of tissues within the area of interest. When compared to the radio treatment, the PDT mode of action comprises of the application of electromagnetic radiation to create radical species in situ. It is a much gentler method for the therapy of cancer and the motive lies in the blend of the action mode of PC used, which are non-noxious in the absence of simulating light and the in situ stimulation by comparatively extended wavelength, visible light [1]. In this section, the detailed application of different MNPs for PDT of tumour cells from preceding studies will be assessed. Silica layered IONPs, which were entangled in the interior of niosomes (SiO/NiO) or fluorescein (FL) entrapped magnetosomes were employed in vitro for PDT of Panc 1 cells, which were irradiated with blue lights. Upon the FL-magnetosomes photoactivation, elevated O2 was created and there was increased magnetically cellular uptake from the Panc 1 cells by the magnetosomes. The effectiveness of the PDT in cells treated with the FL-enmeshed magnetosomes and light was improved with magnetic support [72]. To improve the TRC impact of PDT on tumour hypoxia and ROS brief half-life with a small diffusion distance, a multifunctional nano-platform was created to improve the oxygen intensity in the cancer cells and decrease the ROS distance via the Fenton reaction. The NPs (Fe3 O4 @Dex-TPP) were created via the coprecipitation technique and the PCs (protoporphyrin IX (PpIX) and glutathione-responsive mPEG-ss-COOH) were subsequently embedded into the Fe3 O4 @Dex-TPP to form Fe3 O4 @Dex-TPP/PpIX/ss-mPEG NPs. The created NPs were reported to be effective in the Fenton-supported PDT of cancerous cells. Results also show that the cytotoxic assessment of the NPs on normal endothelial cell (EC) and murine breast cancer (4T1) cells with and without laser light of 637 nm, showed that the noxiousness of the NPs treatment without the laser light was negligible, with cell viability of > 90% for EC, but it was lethal for 4T1 cells as the concentration was increased. While the cell viability for 4T1 was approximately 77% and 50% when the concentration of the NPs was greater than 200 and 25 μg/mL (concentration of PpIX was 20 and 2.5 μg/mL) when treated with laser light of 637 nm. The results showed that the created NPs cyto-compatibility was useful for regular cells but was noxious to cancer cells [73]. Fabricated multi-purposeful NPs (Fe3O4) coupled with a PC (chlorin e6Ce6) and tumour targeting molecules (FA) were employed for the selective aiming of tumour cells (prostate adenocarcinoma (PC-3) and breast adenocarcinoma (MCF-7)) treated with 600 nm wavelength using PDT. Utilizing Fe3 O4 -Ce6-FA, the viability of the cells surpassed 95%, which was indicative of no cytotoxicity in all cells and with exceptional biocompatibility use (Fig. 12a). With the irradiation of both cancerous cells which were inoculated with different concentrations of Fe3 O4 -Ce6-FA for 2 h, the viabilities of the cell lines were drastically reduced with the increase in the concentration of NPs. This showed that the NPs were effectively viable in the treatment of cancerous cells and which were concentration-reliant (Fig. 12b) [74].


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While in the study by Choi et al. [75], FA and hematoporphyrin (HP) were coupled on multi-useful MNPs to create CoFe2 O4 -HPs-FAs which was employed as an efficient anti-tumour reagent for PDT in PT cells (PC-3). It was reported that the same fluence at various times of exposure led to the anti-tumour actions on PC-3 cells and the creation of the reactive O. While in the studies by Li et al. [76], Wang et al. [77], Ashkbar et al. [78], and Wu et al. [79], various MNPs coupled with different photo-sensitizer were synthesized and tailored towards various cancerous cells to assess their biocompatibility and cellular uptake using the PDT coupled with other methods exposed to laser light. It was reported in these various studies that the MNPs coupled with various PCs showed a significant effect on cell reduction and were effective for their tumour cell treatment. Hence they are an exceptional device for greatly preventing cancer development using the PDT coupled with other techniques. Table 1 gives a summary of other studies carried out using the MHT, MRI, PTT and PDT techniques for effective cancer cell eradication employing MNPs. Table 1 Summary of various studies employing TRC techniques for effective cancer diagnosis and treatment using MNPs MNPs

Cancer cells type

TRC technique employed for cancerous cells


Poly(maleic anhydride-alt-1-octadecene) (PMAO) functionalized with glucose

Murine model of pancreatic cancer



MNP-based miRNA

GBM cells (U87-EGFRvIII)




brain and prostate tumours



Iron oxide nanoflowers

Lung cancer cell lines




Tumour necrosis



Bimagnetic Fe/Fe3O4 core/shell nanoparticles

Subcutaneous mouse melanomas (B16-F10)



SP polystyrene-sulfonic-acid-coated magnetic nanoparticles (PSS-MNPs)

SK-Hep1 hepatocellular MHT carcinoma (HCC) cells



Prostate and recurrent brain tumours


Multi-layer β-cyclodextrin and F127 polymer-coated MNPs

A2780CP ovarian MRI cancer cells, MDA-MB-231 (breast), and PC-3 (prostate) cancer cells


Magnetic glyco-NPs (MGNPs)

Cancerous cells





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Table 1 (continued) MNPs

Cancer cells type

TRC technique employed for cancerous cells


PEGylated L-arginine modified IONPs (PEG-Arg@IONPs)

The human foreskin fibroblast (HFF2) cell line and Human embryonic kidney (HEK293) cell





Pc 4 encapsulated into the M4E control cells and PDT ligand-coupled IONPs (Fmp-IO-Pc integrin β1 knock-down 4) M4E derivatives (M4E-15)


Magnetically targeted NPs (IRFes) Breast cancer 4T1 cells

5 Conclusion Over the years, the study of magnetic particle applications in tumour identification and therapy has progressed, but there has only been recent momentous advancement in this research area employing NT. With biomedical applications in the TC of different diseases like cancer, MNPs have proven to be an outstanding contender in meeting the increased global TC needs for improved human healthcare. The improved ratio of the surface area to volume of most NMs built with biomolecules improved the specificity of the chemical drug complex utilized in target treatment and hence improving the efficiency of NMs-based therapy for cancer cells treatment while decreasing their noxiousness to regular cells. With payload capacity improvement, and enhancing their specificity and affinity to aim for tumour cells, MNPs could become appropriate for their utilization clinically with combined tomography and treatment with a great effect and effective result in cancer therapy. Though significant works have been made with the use of MNPs for contemporary and effective tumour treatments, there is still far more to be learned about the safety of NMs applications in TCR to improve life-expectation and prodding tumour patient existence.

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Magnetic Nanomaterials for Heavy Metals Detection Ikenna Chibuzor Emeji, Chike George Okoye-Chine, Orlando Garcia-Rodriguez, Ephraim Igberase, and Peter Ogbemudia Osifo

Abstract Although heavy metals (HMs) are naturally present in the environment, human activity has allowed them to enter water, air, and soil, making them a huge global problem. In high quantities, these HMs are equally hazardous to plants and animals. After entering the body, the majority of them bioaccumulate for a longer time, causing various issues. For example, in plants, they can harm water-absorbing roots, leaves, and cell components, or even obstruct photosynthesis and mineral uptake due to drought-induced inhibition. In addition, they can harm the livers, kidneys, and lungs in animals, where they can also cause cancer. The amount, duration, and level of concentration of these HMs all play a significant role in the anomalies they cause. Because of the toxicity, persistence, and non-biodegradability of certain HMs, they are now a global issue. There are several ways that living creatures have been exposed to these HMs, but drinking water is a common source. It is crucial to find and remove these dangerous HMs. Traditional methods have a number of limitations, such as the need for specialized staff and lengthy sample preparation; as a result, magnetic nanoparticles (MNPs) are used because of their extraordinary magnetic capabilities, which showed considerable potential in the sensing of HMs.

I. C. Emeji (B) · E. Igberase · P. O. Osifo Department of Chemical Engineering, Vaal University of Technology, Private Mail Bag X021, Vanderbijlpark 1900, South Africa e-mail: [email protected] C. G. Okoye-Chine Department of Chemical & Life Science Engineering, Virginia Commonwealth University, Richmond, VA, USA O. Garcia-Rodriguez NUS Environmental Research Institute, National University of Singapore, T-Lab Building 5A Engineering Drive 1, Singapore 117411, Singapore © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 U. O. Aigbe et al. (eds.), Magnetic Nanomaterials, Engineering Materials,



I. C. Emeji et al.

1 Introduction Magnetism in materials originates from the spin and orbital movement of electrons. Every substance is composed of tiny building blocks of matter called atoms. Each atom is made up of electrons, which are charged particles and carry electric charges. These electron orbits the nucleus or centre of an atom. Their movement produces electric current and magnetic effect of each electron. The orbital motion of an electron around the nucleus of an atom is analogous to the current in a loop of wire. Hence, the magnetism of the majority of substances cancels out because of the equal amount of electrons that spin continuously in opposite directions. This is why substances like clothing materials and paper are referred to as weakly magnetic. Most of the charged ions in other materials, like iron, cobalt, and nickel, revolve in the same direction. The building block of matter in these materials becomes extraordinarily magnetic as a result, yet they are not magnets. Nanomaterials (NM) were first defined as substances with at least one constituent particle having an exterior dimension of 100 nm (nm) or less. A nanometer equals one billionth of a meter. Nanoscale, scales nanometers or microns as its units of measurement. The number of dimensions that are larger than 100 nm (nanoscale) can be used to classify NM. As a result, all dimensions within the nanoscale range are classified as zero dimensions (0D). In zero-dimensional NM, none of the dimensions is larger than 100 nm. 0D NM are typically nanoparticles (NPs). Another type is one dimension NM, which is outside the nanoscale. One-dimensional NM (1D), include nanowires, nanorods, and nanotubes. Non-confinement of two dimensions to the nanoscale is the major characteristic of two-dimensional (2D) NM. Structurally, 2D- NM has plate-like forms and they include graphene, nanofilms, nanolayers, and nanocoatings. Outside of the nanoscale is the three-dimensional NM (3D). In 3D all materials are not confined to the nanoscale in any dimension. Large-proportion powders, nanoparticle dispersions, and a bunch of nanowires and nanotubes, including multi-nanolayers, can all be found in this class. NM can further be divided into subcategories like organic-based, inorganic-based, carbon-based, and composite-based. As demonstrated in Fig. 1 as adapted from [1], organic materials such as dendrimers, cyclodextrin, polymers, liposomes, and micelles, are used to create organic-based NM [1]. Dendrimers, on the other hand, are branched unit-based nanosized polymers. Meanwhile, metal-based NMs and metal oxide-based NMs are included in inorganic-based NMs (Fig. 2). Silver, gold, aluminium, cadmium, copper, iron, zinc, and lead are all examples of metal-based inorganic NM [2], whereas metal oxidebased inorganic NM [3] are zinc oxide (ZnO), Quantum dots, copper oxide (CuO), nanogold, magnesium aluminium oxide (MgAl2 O4 ), nanosilver, and titanium dioxide (TiO2 ), iron oxide (Fe2 O3 ), cerium oxide (CeO2 ), and silica (SiO2 ). Additionally, carbon-based NMs [4] are a special category of NM consisting of carbon atoms and they include, carbon nanotubes, graphene, multiwalled carbon nanotubes, nanodiamond, carbon nanotubes (CNTs), single-walled carbon fiber, activated carbon, and carbon black (see Fig. 3 as adapted from [4]). The mixture of metal,

Magnetic Nanomaterials for Heavy Metals Detection


Fig. 1 Organic-based NM

Fig. 2 Types of inorganic metal nanoparticles (MNP)

metal oxide, carbon, or organic NM is referred to as a composite nanomaterial, and these NM feature intricate structures, such as a metal–organic framework. In applications across numerous industrial sectors, purposefully synthesized MNPs with distinctive thermal, mechanical, medicinal, and commercial attributes are greatly sought after. In this chapter, we will discuss how these MNPs are utilized to detect and eliminate HMs from the environment. Their advantages over conventional heavy metal detection will also be emphasized.


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Fig. 3 Various forms of carbon NM

2 HMs The term “HMs” has been defined differently by several writers. Their meanings vary depending on the specific weight, atomic weight, atomic number, metal density, particular chemical properties, and toxicity [5]. Very recently, Ali and Khan, [6] defined “heavy metal” in a more acceptable scientific way, as metals in nature, having an atomic number (Z) greater than 20 and a density which is primarily higher than 5 g cm−3 . Due to their functions in biological systems, HMs can be roughly divided into two major groups: essential and nonessential HMs. While nonessential HMs are not required by living things, not even at trace levels, essential HMs are very necessary for organism functionality and may even be needed for body chemistry at low concentrations [7]. However, the earth’s crust naturally contains HMs. Actinides, lanthanides, transition metals, and a number of metalloids are among the more than 50 elements that fall under the category of HMs. Of those elements, 17 are considered to be extremely hazardous and easily accessible. The toxicity of several non-essential HMs, like Pb, Hg, As, Cr, Tl, and Cd, is quite high even at low concentrations [8, 9]. Other HMs that are necessary for human nutrition include Cu, Zn, Ni, Co, Se, and Bi, but they can also be hazardous in higher concentrations. HMs toxicity varies with concentration, exposure time, and method of exposure. Biological, geological, and human activities are all potential sources of HMs pollution of the environment (Fig. 4). The wearing action on metal-bearing rocks, soil erosion of metal ions, volcanic eruptions, and forest fires are some of the geological processes that cause HMs to enter the environment [10]. HMs in the environment are a result of growing industrialisation and urbanization, which are anthropogenic sources. These metals are discharged as a result of human activities such as mining and extracting various

Magnetic Nanomaterials for Heavy Metals Detection


Fig. 4 Sources of HMs within the environment

elements from their respective ores, releasing domestic and industrial sewage into the environment, applying organic and inorganic fertilizers, allowing urban runoff, and burning fossil fuels [11]. Non-essential, poisonous HMs have the potential to cause cancer, are they are not biodegradable and have a propensity to build up in living things. All of these metals are mostly acquired by the general public through the air, drinking water, and food, with fish serving as the most important source of origin for mercury exposure. Additionally, smokers are not protected from cadmium at significant levels [12].

3 HMs Detection At high concentrations, all metals or elements are poisonous [5]. Their nonbiodegradability and bioaccumulation amplify risks and concerns, thus appropriate procedures must be developed for their prompt identification to prevent issues with the environment and human health. High-performance liquid chromatography (HPLC) combined with electrochemical or UV–Vis detectors, UV/Vis spectroscopy, atomic absorption spectroscopy (AAS) [13, 14], inductively coupled plasma mass spectrometry (ICP-MS) [15], flame atomic absorption spectrometry,


I. C. Emeji et al.

microprobes (MP), anodic stripping voltammetry (ASV), and wet chemical methods like colorimetry and electrochemical techniques [16] are comprehensively the most used methods for the sensing of HM ions. However, there are a number of disadvantages to these analytical techniques such as sample development, cleanup, preconcentration steps, high-cost equipment, and a specialized workforce. Due to their great adsorption capacity, high surface-to-volume ratio, strong surface reactivity, size-controlling features, high catalytic effectiveness, and high level of functionalization, MNPs have recently shown tremendous potential in the sensing of HMs. MNPs utilization as nanosensors has enhanced sensitivity and selectivity [17]. The most common varieties of MNPs are often a class of NM that is made up of metals like cobalt, nickel, and iron with unique features such as paramagnetic, ferromagnetic, superparamagnetic, and high surface-to-volume ratios. These characteristics make it possible to use them in the creation and manufacturing of sensors for various purposes. In order to create specific nano sensors for the wholesome sensing of harmful metal ions, a variety of magnetic NM should be involved and employed.

3.1 Sensors for Sensing HMs It is crucial to remember that the primary function of MNPs in the identification and removal of HMs is to achieve magnetic separation where a magnetic field is present. Due to their superior magnetic properties, iron oxide, which is found in the forms of hematite (α-Fe2 O3 ) and magnetite (Fe3 O4 ), is the most often utilized MNPs for the detection of HMs. Because iron oxide NPs tend to cluster readily and become nonconductive, very few researchers have employed iron oxide alone to sense HMs. Therefore, to decrease the likelihood of aggregation, the majority of research either uses surface modification paired with additional materials or functionalization. As described in Table 1, different kinds of biosensors shown were synthesized for the identification and removal of HMs from the environment. For the detection, adsorption, and separation of cadmium (Cd2+ ) metal ions in a water sample, Zhang et al. [18] produced MNPs Fe3 O4 @FePO4 with core–shell structure by coating Fe3 O4 NPs with iron phosphate by liquid phase deposition method. A sensor constructed of Fe3 O4 /TiO2 /NG/Au/ETBD was also created by Liu and colleagues [19] precisely to detect Pb2+ in a highly hazardous aquatic environment. A greater linear range of sensitivity from 40 × 10−14 mol/L to 20 × 10−9 mol/L was possible with the sensor as-designed. Pb2+ had lower limits of detection that were 75 × 10−14 . Additionally, Fe3 O4 NPs are simple to coat with polydopamine to create stable core–shell bifunctional polydopamine@Fe3 O4 NPs, which are then used to conveniently modify the surface of magnetic glassy carbon (mGC) electrodes in order to sense Pb2+ and Cd2+ with high responsiveness using square wave anodic stripping voltammetry (SWASV) [20]. By covering the simple screen-printed electrode (SPE) with a solution of Fe3 O4 and Chitosan (CHT) on an ionic liquid (IL), Wang et al. [21] effectively created a sensor. This is accompanied by the in-situ deposition of a bismuth film (Bi). The

Magnetic Nanomaterials for Heavy Metals Detection


authors claim that the as-created bismuth film/Fe3 O4 /IL composite functionalised screen-printed electrode has the lowest Cd2+ detection limit of 0.5 × 10–1 g/L. In addition to magnetic iron oxide NPs, nickel oxide and cobalt oxide NPs can be used to create several types of sensors whose application in the environment is the identification of HMs. Owing to the characterization of high activity and exceptional stability, cobalt oxide has garnered interest. Salimi and co-workers [22] doped cobalt oxide NPs on a modified glassy carbon electrode to create a sensor, which they utilized to detect a very small amount of the arsenic (As3+ ) ion in an aqueous solution. With a progressive range of 10–50 μM, a modified electrode dramatically displayed a detection limit of 6 × 10–1 μM with no intrusion but other NM ions are present. Additionally, Hosseini and associates [23] created a sensitive colorimetric sensor for the detection of dopamine based on the cobalt-doped magnetite/graphene nanocomposites (Co-MGNCs) peroxidase mimetic. The created sensor exhibits excellent linear correlations for dopamine concentrations between 0.5 and 50 mM. The relative standard deviation (RSD) was below 4.0%, and the limit of detection was calculated to be 0.08 mM. Kumar and coworkers [24] developed graphene oxide and nickel tungstate (RGO@NiWO4 ) NCs, for selective and continuous identification of HM ions in drinking water and also in complex aqueous media such as milk, fruit juices, and carbonated beverages. They obtained a lower limit of detection for Cd2+ , Cu2+ and Hg2+ ions to be 47 × 10–11 M, 38 × 10–11 M, 44 × 10–11 M and 28 × 10–11 M for individual detection and 10 × 10–11 , 18 × 10–11 , 23 × 10–11 and 28 × 10–11 M respectively. In 2017, Dong and Zhang [25] developed a magnetic composite sensor Table 1 HMs from the environment resourced by nanosensors Nanosensors

HMs selectivity

Fe3 O4/ TiO2/ NG/Au/ ETBD


75 ×

Fe3 O4 -NPs/TA/GCE

Cd2+ , Pb2+ and Hg2+

2.25 × 101 , 8.30 and 6.02 × 101 μg L−1


Fe3 O4 @FePO4


10 μg L−1


Co3 O4 nanosheets/ ITO


5.20 × 10–1


rGO-Fe3 O4 /SPE


1.0 × 10–1


Bi/Fe2 O3 /G/GCE

Cd2+ ,

8.0 × 101 ; 10 × 101 and 7.0 × 10–2


Balls NiO-GCE

Cd2+ , Pb2+

16.6 and 7.90 μg L−1




12.4 × 10–3 μg L−1


Bi/Fe3 O4 /ILSPE


0.05 μg/L


ILs/NiCo2 O4 -P

Tl+ , Pb2+ and Cu2+

0.046, 0.034 and 0.029 μg/L




94 μg L−1



Cd2+ ,

47 × 10–11 M, 38 × 10–11 M, 44 × 10–11 M and 28 × 10–11 M





Pb2+ ,

Cu2+ and Hg2+

Limit of detection 10−14


References [19]


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(ILs/NiCo2 O4 -P) for the continuous measurement of the metals thallium (Tl+ ) lead (Pb2+ ), and copper (Cu2+ ) ions by coupling the porous magnetic nickel cobaltate (NiCo2 O4 ) with ionic liquids (ILs) as modified materials. The censoring limit of the created electrode were 0.046, 0.034, and 0.029 g/L for the given metals of Tl+ , Pb2+ , and Cu2+ ions, respectively, using differential pulse anodic stripping voltammetry (DPASV). According to Ndlovu et al. [26] exfoliated graphite (EG) electrode, was modified with cobalt oxide NPs (CoOxNPs) to fabricate an electrochemical sensor which was used to sense Cu2+ in spiked water samples. A low limit of detection of 94 μg L−1 was recorded.

4 Conclusion Magnetic NM-based sensors for HMs detection were covered in this chapter. Because of its special characteristics, using nanotechnology to sensor HMs from the ecosystem is gaining a lot of attention. Since NM is incorporated with the sensor architecture, selectivity and sensitivity for detecting HMs within the environment have also improved. The advantages of using nanosensors based on functionalized NPs over traditional methods are more, among which are low cost, low limit of detection, and convenience of usage in the field of applications. Since the development and usage of magnetic nanosensors, on-site identification capability, sensitivity, mobility, and overall achievement have all been enhanced in detecting HMs in the environment. Although unimaginable revolutions and advances have been made, the detection of these HM ions using nanosensors still faces significant technological obstacles when applied to real-world samples like biological and raw water samples. To fully utilize the developing potential of nanosensors to detect HMs in the environment, cooperation between research societies, governments, and enterprises is required.

References 1. Gessner, I., Neundorf, I.: Nanoparticles modified with cell-penetrating peptides: conjugation mechanisms, physicochemical properties, and application in cancer diagnosis and therapy. Int. J. Mol. Sci. 21(7), 2536 (2020) 2. Li, W., Cao, Z., Liu, R., Liu, L., Li, H., Li, X., Chen, Y., Lu, C., Liu, Y.: AuNPs as an important inorganic nanoparticle applied in drug carrier systems. Artif. Cells Nanomed. Biotechnol. 47(1), 4222–4233 (2019) 3. Emeji, I.C., Ama, O.M., Aigbe, U.O., Khoele, K., Osifo, P.O., Ray, S.S.: Properties and synthesis of metal oxide nanoparticles in electrochemistry. In: Nanostructured Metal-Oxide Electrode Materials for Water Purification, pp. 85–96. Springer, Cham (2020) 4. Yan, Q.L., Gozin, M., Zhao, F.Q., Cohen, A., Pang, S.P.: Highly energetic compositions based on functionalized carbon nanomaterials. Nanoscale 8(9), 4799–4851 (2016) 5. Hodson, M.E.: Heavy metals—geochemical bogey men? Environ. Pollut. 129(3), 341–343 (2004)

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6. Ali, H., Khan, E.: What are heavy metals? Long-standing controversy over the scientific use of the term ‘heavy metals’–proposal of a comprehensive definition. Toxicol. Environ. Chem. 100(1), 6–19 (2018) 7. Ali, H., Khan, E., Ilahi, I.: Environmental chemistry and ecotoxicology of hazardous heavy metals: environmental persistence, toxicity, and bioaccumulation. J. Chem. (2019) 8. Rahimi, M., Jafari, O., Mohammdifar, A.: Intensification of liquid-liquid mass transfer in micromixer assisted by ultrasound irradiation and Fe3O4 nanoparticles. Chem. Eng. Process. 111, 79–88 (2017) 9. Zhang, Z., Chen, K., Zhao, Q., Huang, M., Ouyang, X.: Comparative adsorption of heavy metal ions in wastewater on monolayer molybdenum disulfide. Green Energy & Environ. 6(5), 751–758 (2021) 10. Tchounwou, P.B., Yedjou, C.G., Patlolla, A.K., Sutton, D.J.: Heavy metal toxicity and the environment. Mol. Clin. Environ. Toxicol. 133–164 (2012) 11. Qiao, Y., Yang, Y., Gu, J., Zhao, J.: Distribution and geochemical speciation of heavy metals in sediments from coastal area suffered rapid urbanization, a case study of Shantou Bay, China. Marine Pollut. Bull. 68(1–2), 140–146 (2013) 12. Järup, L.: Hazards of heavy metal contamination. Br. Med. Bull. 68, 167–182 (2003). https:// 13. Kenawy, I.M.M., Hafez, M.A.H., Akl, M.A., Lashein, R.R.: Determination by AAS of some trace heavy metal ions in some natural and biological samples after their preconcentration using newly chemically modified chloromethylated polystyrene-PAN ion-exchanger. Anal. Sci. 16, 493–500 (2000). 14. Pohl, P.: Determination of metal content in honey by atomic absorption and emission spectrometries. Trends Anal. Chem. 28, 117–128 (2009). 09.015 15. Silva, E.L., dos Santos Roldan, P., Giné, M.F.: Simultaneous preconcentration of copper, zinc, cadmium, and nickel in water samples by cloud point extraction using 4-(2-pyridylazo)resorcinol and their determination by inductively coupled plasma optic emission spectrometry. J. Hazard. Mater. 171, 1133–1138 (2009). 16. Emeji, I., Ama, M.O., Osifo, P., Ray, S.S., García-Rodríguez, O., Lefebvre, O.: Electrochemical preparation of iron-supported carbon-cloth electrode and its application in the in-situ production of hydrogen peroxide (2019) 17. Borah, S.B., Bora, T., Baruah, S., Dutta, J.: Heavy metal ion sensing in water using surface plasmon resonance of metallic nanostructures. Groundw. Sustain. Dev. 1(1–2), 1–11 (2015) 18. Zhang, X., Sun, C., Zhang, L., Liu, H., Cao, B., Liu, L., Gong, W.: Adsorption studies of cadmium onto magnetic Fe3 O4 @FePO4 and its preconcentration with detection by electrothermal atomic absorption spectrometry. Talanta 181, 352–358 (2018) 19. Liu, F.M., Zhang, Y., Yin, W., Hou, C.J., Huo, D.Q., He, B., Qian, L.L., Fa, H.B.: A high– selectivity electrochemical sensor for ultra-trace lead (II) detection based on a nanocomposite consisting of nitrogen-doped graphene/gold nanoparticles functionalized with ETBD and Fe3O4@ TiO2 core–shell nanoparticles. Sens. Actuators B Chem. 242, 889–896 (2017) 20. Song, Q., Li, M., Huang, L., Wu, Q., Zhou, Y., Wang, Y.: Bifunctional polydopamine@Fe3O4 core-shell nanoparticles for electrochemical determination of lead(II) and cadmium(II). Anal. Chim. Acta 787, 64e70 (2013). 21. Wang, H., Zhao, G., Yin, Y., Wang, Z., Liu, G.: Screen-printed electrode modified by bismuth/ fe3o4 nanoparticle/ionic liquid composite using internal standard normalization for accurate determination of Cd (II) in Soil. Sensors 18(1), 6 (2017) 22. Salimi, A., Mamkhezri, H., Hallaj, R., Soltanian, S.: Electrochemical detection of trace amount of arsenic (III) at glassy carbon electrode modified with cobalt oxide nanoparticles. Sens. Actuators B Chem. 129(1), 246–254 (2008) 23. Hosseini, M., Aghazadeh, M., Ganjali, M.R.: A facile one-pot synthesis of cobalt-doped magnetite/graphene nanocomposite as peroxidase mimetics in dopamine detection. New J. Chem. 41(21), 12678–12684 (2017)


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Magnetic Nanomaterials for Dye Sensing and Removal Joan Nyika and Megersa Olumana Dinka

Abstract Varied applications of nanomaterials have transformed various industries in the modern day. In recent years, magnetic nanoparticles (MNPs) have gained research interest from their applications in the environmental, agricultural, catalysis, medical and biosensing fields. This chapter explored the potential of MNPs in dye sensing and removal using pre-existent studies. Findings showed that MNPs are widely used in sensing various ionic and non-ionic dyes such as the azo, acid, cationic, reactive and dispersive dyes. The sensing and removal abilities were associated with the superparamagnetic, high surface area and adsorptive characteristics of MNPs. The characteristics can be improved and customized using controlled surface engineering to produce functionalized nanomaterials with high sensitivity to specific dyes. Optimizing the dye concentration, pH, temperature and adsorbent quantity can further optimize the dye sensing and removal capacities. The chapter aimed at assessing the potential of MNPs in dye sensing and removal for greener remediation of pollutants. Keywords Biosensing · Dye · Magnetite · Nanomaterials · Superparamagnetism

1 Introduction The nanotechnology field has had significant advancements in the modern day, which have revolutionized and improved varied fields. The list of applications of the technology is growing exponentially with the use of nanomaterials and nanoparticles J. Nyika (B) · M. O. Dinka Department of Civil Engineering Science, University of Johannesburg, Johannesburg, South Africa e-mail: [email protected] M. O. Dinka e-mail: [email protected] J. Nyika Deapartment of Geosciences and the Environment, Technical University of Kenya, Nairobi, Kenya © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 U. O. Aigbe et al. (eds.), Magnetic Nanomaterials, Engineering Materials,



J. Nyika and M. O. Dinka

[1, 2]. Nanomaterials are minute particles whose average sizes are 1–100 nm and making them ideal for a variety of applications. Among the nanoparticles, MNPs have recorded growing environmental, engineering, energy and biomedical applications owing to their nanoscale and exceptional characteristics [3]. Consequently, MNPs have gained the attention of scientific researchers owing to the potential used in agriculture, environment, biomedicine, biosensing and catalysis among other fields [2–6]. Figure 1 shows the applications of various MNPs as adopted from the publications of [1, 3, 5–12]. To advance the agricultural sector, magnetic nanomaterials have been used to manufacture nano-herbicides, nano-pesticides, nano-sensors, nanoadditives and nano-fertilizers aimed at improving crop productivity and concurrently, enhancing the resilience of plants to pests and diseases [7]. MNPs have been applied in environmental clean-up to remove organic and inorganic pollutants from wastewater [8]. In biomedicine, MNPs have been used in drug encapsulation and release, gene therapy, radioimmunotherapy, drug delivery and formulation, chemotherapy and in hyperthermia treatment [8]. MNPs are also important components of electrochemical, optical and piezoelectric biosensors whose functioning can incorporate catalytic or non-catalytic reactions [9]. MNPs occur in different types but the superparamagnetic magnetite made of iron oxide (Fe3 O4 ) is the commonest in all applications. In the field of biosensing that deals with the discovery of organisms and quantification of their physiological activity, MNPs are growing to be essential replacements for conventional labels owing to their unique aspects not present in many biological systems [1, 9, 13]. As such, there is a need to understand their properties to match them with the particular application of target.

Fig. 1 Varied applications of MNPs

Magnetic Nanomaterials for Dye Sensing and Removal


This is the rationale in this chapter where we examine the types and properties of MNPs and matched them with their intended use in sensing and removing dyes from the environment. The significance of such advances is to inform decisions on making shape-controlled, mono- or multi-dispersed nanomaterials whose structural design fits the intended use or is customized for the particular use. Overall, this increases the effectiveness of MNPs for sustainable environmental management. This chapter explored the types of MNPs, their characteristics and their application in biosensing and in particular, dye sensing using Fe3 O4 nanoparticles based on preexistent literature.

2 Types of MNPs and Their Properties 2.1 Types of MNPs There are three types of MNPs: oxides, metals and alloys. Oxides have fluctuating magnetic characteristics, which are antiferromagnetic. Oxides of cobalt (CoO, Co3 O4 ) and iron (FeO) are the most significant magnetic particles [14]. Cobalt tetroxide (Co3 O4 ) has magnetic properties that change under varied conditions. The material shows antiferromagnetic characteristics with bulk magnetic circulation while at 0.02 emu/g to 10kOe magnetic circulation, it has weak ferromagnetic characteristics [15]. Once exposed to magnetic fields, Co3 O4 acts like a typical magnet but with weak ferromagnetic tendencies. CoO also has variable magnetic characteristics like loop shifts, coercivities and large movements, which are anomalous magnetic features [14]. Nanoparticles from FeO particularly maghemite (γ-Fe2 O3 ) and Fe3 O4 are also widely used due to their superparamagnetic characteristics including their ability to cause energy release, particle movement and image contrasting when an external magnetic field is availed [10]. Metals such as nickel (Ni) have both catalytic and magnetic properties and are suitable for MNPs. Ni-NPs are of great interest in research for use as biosensors, photocatalysts, heat exchangers and electrocatalysts [16]. The nanomaterial is synthesized using photocatalytic reduction, discharge route and chemical reduction techniques. Additionally, some of the synthesis methods applied for all MNPs, in general, include biological processing, sol–gel, gas-phase condensation, microemulsion synthesis, hydrothermal synthesis, thermal decomposition and ball milling [1]. The magnetic properties of Ni-NPs are dependent on their morphology, compounds containing the element and their lattices [17]. The size of the nanomaterial also influences its characteristics. According to He et al., “the Curie temperature, saturation magnetization and remanent magnetization increase whereas the coercivity decreases monotonously with the increase of particle size” for Ni-NPs. Therefore, larger particles of Ni have higher palaeomagnetism and saturation levels compared to smaller ones.


J. Nyika and M. O. Dinka

Metallic alloy NPs are a result of combining two or more metals and unlike monometallic NPs, they are more effective due to synergistic properties. They are formed by melting the constituent metals and mixing them in protective conditions such as the presence of argon gas. The approach was used to synthesize the Fe56Co7Ni7B20Nb10 alloy whose properties are diverse and complex due to its heterogeneous and multi-metal nature [18]. In another study, Lutz et al. [19] noted that alloy-based NPs possessed superparamagnetic characteristics from metallic and oxide nanomaterials.

2.2 Properties of Magnetic Nanomaterials Using instruments such as Mossbauer Spectroscopy (MS), Transmission Electron Microscopy (TEM), Fourier Transform Infrared (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-RAY Diffraction (EDXD), X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM), various properties of MNPs have been identified [1, 20]. The aim is to determine the variations in nanomaterials as a result of changes in physicochemical aspects and use them for optimization geared to their specific applications. Such variations are in the surface morphology, size, structure, type of bonding and elemental composition of the MNPs. MNPs have a stable metallic core and they are functionalized by an outer shell addition that has functional groups depending on the targeted use. They have a size < 100 nm and can be synthesized from any material with magnetism ability. Metallic cores of MNPs are made of mainly oxides of iron; γ-Fe2 O3 and Fe3 O4 . Most MNPs are responsive and stable single-domain structures positioned in settings surpassing Curie temperatures (TC ), which makes them superparamagnetic nanomaterials (SPNs) [11]. Such SPNs have a high magnetic attraction, low agglutination ability at room temperature, low coercivity and low remanence [11]. The magnetism of MNPs is a result of magnetic spin moments by holes, electrons, protons, and positive and negative ions that have electrical resistance and mass. Different nanomaterials show varied categories of magnetism. The categories include ferromagnetism, paramagnetism, superparamagnetism, diamagnetism and/ or antiferromagnetism and are distinguishable as shown in Fig. 2 as adapted from [21]. The formation of internal-based magnetic fields that are parallel to the applied magnetic domains for nanomaterials with unpaired electrons is paramagnetism [11]. Ferromagnetism depends on the TC and the critical value (DC ) and occurs when ferromagnets separate into smaller magnetic domains whose diameter is smaller than the DC [12]. The DC of a nanomaterial is dependent on the shape of particles, the energy of a domain-wall or surface, the strength of exchange forces and crystal anisotropy and the magnetic saturation value. Superparamagnetism is a form of ferromagnetism, which occurs when one domain of ferri- and ferro-magnetic materials have a diameter of 3–50 nm, which is smaller than the DC [4]. Superparamagnetic nanomaterials have strong thermal effects and can demagnetize already saturated assemblies, and have zero hystereses and coercivity [12]. The TC and DC of MNPs differ based on the

Magnetic Nanomaterials for Dye Sensing and Removal


specific nanomaterial as evident in Table 1 [11]. Diamagnetism is a weak repulsion to magnetic domains exhibited by all materials when their electronic subshells are full and magnetic moments cancel each other after pairing [21]. Antiferromagnetic materials have an antiparallel atomic magnetic moment of similar magnitude and hence, a total magnetization of zero [21]. Apart from the magnetic effect of MNPs, such materials exhibit the magnetocaloric effect, which refers to the heating up of magnetic particles in a magnetic field and then cooling it [22]. Due to their large surface area, MNPs exchange heat with their environs easily and hence the need to modify their structures to core-shells that have controlled heat exchange. The magnetocaloric effect is usually applied in various biomedical therapies [22].

Fig. 2 Illustration of different types of magnetism exhibited by magnetic nanomaterials based on their specific spin moment direction

Table 1 Different magnetic nanomaterials and their Curie temperatures and critical values Material

Type of magnetism

DC (nm)

Curie temperature (K)

Europium oxide (EuO)


11 corresponds to MI concentrations [94]. As observed in Table 4, the sorption of most MI species was enhanced with increasing pH, with the sorption of most pollutants taking place with the pH range of 2–9.6. The mechanism of MI uptake varied at different pH values as the solution pH impacts the structure of the sorbent surface and the sorbate structure present in an aqueous-medium [99].

4.2 Influence of Sorbent Dose In studying the sequestration of contaminants from industrial effluent, a key factor is the sorbent dose, which is required to select the ideal sorbent dose to decrease the treatment process cost [98]. The extent of contaminants confiscated by the SP is directly proportional to the amount of sorbent utilized [21, 100]. As reported in the studies of Babudurai et al. [101], Horst et al. [6], Nodeh et al. [102], Kataria et al. [103], Safari et al. [104], Wen et al. [105], Zhao et al. [50], Oukebdane et al. [106], Kumari et al. [107], and Panahadeh et al. [40], improvement in the sorbent dosage led to an increase in the number of active sites on the sorbent surface for sequestrating HMs and dyes, thereby causing a considerable increase in the percentage (%) of confiscation of pollutants. With a subsequent rise in the sorbent dosage, there is a reduction in the active sites owing to the decrease in the sorbent surface-area, which is heightened by the enhancement in the number of NPs present owing to aggregation, and this greatly decreases the % of pollutants removed. Research papers reviewed showed that improvement in the sorbent dose led to an

Applications of Magnetic Nanomaterials for Wastewater Treatment


improved confiscation of contaminants owing to the improvement in the surface-area of the sorbent and hence an enhanced number of accessible active sites available on the sorbent surface for the SP.

4.3 Influence of Contact Time Another critical factor in the SP which is employed to predict the mechanism of sorption is the contact time that is mandatory for the confiscation of different contaminants from effluents onto the sorbent material [98]. From the commercial and technological point of view, sorption time as a performance factor is important. Hence, contact time optimization will lead to the creation of an applicable technique for contaminants treatment and can also be efficient in assessing water and effluent treatment costs [97]. Generally, the extended contact time of the SP enhances the SC and the efficiency of pollutant confiscation. At the beginning of the SP, the quantity of pollutants sorbed to the surface of the sorbent increases fast and slows down and achieves equilibrium after some time. This is attributed to the quantity of the sorbed pollutant at the dynamic equilibrium phase. The critical contact time to attain the stability state is known as the stability time and the quantity of the sorbed pollutant at the stability time mimics the ultimate sorbent material sorption rate under the operational requirements [21, 50, 95, 100, 102, 103, 106].

4.4 Influence of Initial Sorbate Concentration A vital energetic force that is delivered to enhance mass transfer resistances of pollutant molecules between the water-soluble medium and the solid phase is the initial concentration. At minimal concentrations, the proportion between the preliminary quantity of pollutants molecules to the accessible sorbent surface-area is low and hence, the sorption rate is not affected by the preliminary pollutant concentration. However, the unoccupied sorption sites become fewer at higher pollutant concentrations and thus, the rate of pollutants confiscation depends on the initial pollutant concentration [95]. Normally, the stability of the SC enhances with rising contaminant concentration, which is suggestive that a higher preliminary contaminant concentration will improve the SP. But the percentage of pollutants confiscated reduces with improved initial contaminant concentrations [50, 98, 103, 106, 108–110].


U. O. Aigbe et al.

5 Isotherms and Kinetic Models for the SP of HMs and Dyes to Various MNMs Kinetic models define the association between the sorbed sorbate amount (qt ) and the contact time (t) for the SP. Because of chemical reactions’ existence, kinetic projections are important for the design of the sorption system and reaction rate controlling step determination. Furthermore, the nature of sorption changes with the physio-chemical classification of the sorbent and the condition of reactions like pH, ionic strength, dosage, and temperature. The most used kinetic models consist of the PFOR and PSOR, Elovich (ELH) and IND models [15]. The sorption reaction model regulates the sorption functioning and mechanisms. The PFOR was introduced by Lagergren in 1898 to define the process of liquid–solid phase sorption of oxalic acid and malonic acid to charcoal. It is considered as the most basic model relating to the sorption rate based on the SC. While in 1998, Ho define the process of the sorption of divalent MI to peats, in which the chemical bonding between the divalent MI and polar functional groups on peats is liable for the peat cation-exchange capacity. This fundamental theory is that sorption may be secondordered and the rate limiting steps may be chemical sorption connecting valent forces via sharing or interchange of electrons between the peat and divalent MI. Also, Ho’s second-order rate equation (PSOR) is employed to distinguish kinetic equations on the SC for solution concentration. Weber and Morris in 1962, hypothesized that the IND rate changes comparably with the half power of time. According to the theory by Weber and Morris, the limiting step rate is IND, a plot of the solute sorbed against the square root of the contact time will produce a straight line passing via the origin of the graph. However, the rate constant for IND is gotten from the curve incline [111]. The PFOR model is relevant when the percentage of sorption sites occupation is relative to the amount of sorbents’ unoccupied sites. While the PSOR processes are hugely impacted by the number of sorbate ions on the surface of the sorbent and the equipoise concentration of the sorbate ions [98]. The sorbate and sorbent interaction is suggestive of the sorption isotherm and the factors resulting from these different models give facts about the SP. An isotherm is also a critical tool for evaluating the distribution of sorbent over liquid solid borders and their SC assessment. Hence, isotherm research data are employed to create an applicable sorption system [97]. The use of sorbents with a high particular surfacearea involves achieving sorption equilibrium at a rapid time owing to the quicker kinetics for the pollutants’ confiscation. While in the SP, the SC of the nano-sorbents is determined by employing different isotherm models. The most common models that are generally employed to assess the SC are the LGR and the FRH models. The LGR model is essentially associated with the idea that sorption happens on a monolayer and with no additional sorption taking place after saturation [112]. The LGR model was created by Irving Langmuir in 1916 and is the top extensively utilized isotherm model for studying sorption. While the FRH model was proposed in 1991 by Freudlich to explain the mathematical model to a non-linear isotherm, which will result in a clean empirical formula for sorption on multiple sites [41, 98].

Applications of Magnetic Nanomaterials for Wastewater Treatment


Table 3 Kinetic and isotherm models Models

Linear expression


log(qe − qt ) = logqe −


t 1 t qt = k2 qe2 + qe


qt = kF


1 qe


lnqe =



t 1/2

Parameters k1 2.303

qe, qt and k1 indicate the SC at equilibrium (mg.g−1 ), SC at time t (mg.g−1 ) and PFOR rate constant (min−1 ) k2 is the PSOR rate constant (g/mg.min)


1 Qm KL


1 Ce

kF and C denote the IND rate constant (mg.g−1 .min1/2 ) and the intercept of IND +

1 Qm

(Type 2)

(1) n ln(Ce ) + ln(kf )

Qm , KL , and Ce indicate the monolayer SC (mg.g−1 ), sorption equilibrium constant (L/ mg) and sorbate equilibrium concentration (mg/L) n and Kf indicate the FRH constants

The LGR model symbolizes one of the dependable laws of physics regulating the SP, which is centred on the theory that the sorbate is particularly layered and consistent, sorption bonds are flexible and sorption energy is the objective of the sorbed amount of sorbate on the sorbent. While the FRH model adopts that sorption happens on diverse sorbent surfaces and making it appropriate for modest and elevated concentrations and relatively ineffective at reduced concentrations [113–115]. The linearized forms of both models are depicted in Table 3. One of the critical factors in the choice of sorption isotherm and kinetic is the square of correlation coefficient (R2 ) and the closer the value of R2 to 1, the more reliable the acquired experiment data with the respected models [113]. Table 4 shows a summary of research performed for kinetic and isotherm model applications for the sequestration of pollutants using MNMs [15]. The SP of various pollutants to MNMs was mostly ideally defined in the order of PSOR > PFOR and LGR > FRH > LGR-FRH > Koble-Corrigan. The PSOR model is interrelated with the experimental data from reviewed studies, with the chemisorption mechanism being the rate-determining phase, which is considered a chemical reaction between the sorbate and the sorbent. While the LGR model predict the monolayer SP and the surface of the sorbent was homogeneous [1, 98].

6 Thermodynamics The parameters of thermodynamics are extremely considered in defining the SP and achieving an equilibrium state. To ascertain the SP’s spontaneity and feasibility, thermodynamic considerations for sorption research are mandatory. The parameters ◦ of thermodynamics comprise of the change in entropy (△s ), change in Gibb free ◦ ◦ energy (△G ) and change in enthalpy (△H ). The Van’t Hoff equation is employed ◦ ◦ ◦ to determine △s , △G and △H , which gives an understanding of the SP’s nature and mechanism [116].



Kinetic model

Isotherm model/Qm (mg.g−1 )



IO-doped methyltrimethoxysilane (Fe2 O3 -MTMOS)






α − Fe2 O3





Spontaneous and endothermic


Alginate-Based Fe3 O4 –MnO2 xerogel

Cr6+ and Cd2+



FRH/7.24 and 7.79

Spontaneous and exothermic


Unmodified (Fe3 O4 NPs), and modified with poly(sodium acrylate) (Fe3 O4 /PSA NPs)

Zn2+ , Cu2+ , Ni2+ , 3–7 Cd2+ , Pb2+ , Cr3+ , and Cr6+


LGR/4.83,14.24, 5.26, 3.34,45.71, 23.65, 35.22/16.93, 33.44, 17.65, 34.61, 129.10, 39.71, and 39.99


Silica-reinforced IO NCs

Pb2+ , Cd2+ , Cu2+ , Ni2+ , and Zn2+

5 (Pb2+ , Cd2+ , PSOR and Cu2+ ,) and 6 (Ni2+ , and Zn2+

LGR/19.67, 20.56, 22.06, 19.85, and 22.34

Spontaneous and endothermic



Cr6+ , Zn2+ , and Cu2+

Alkaline pH


17.2, 4.8, and 3.9


Polycationic/di-metallic Fe/ Al (PDFe/Al) NCs






Hyperbranched polyglycerol (HPG)-MNPs

Ni2+ , Cu2+ and Al2+



LGR and FRH/0.451, 0.700, and 0.790


Fe3 O4

Pb2+ , Cd2+ , Cu2+ and Ni2+



LGR/85, 79, 83, and 66


Macroporous IO NCs cryogels





[126] (continued)

U. O. Aigbe et al.



Table 4 A summary of the non-exhaustive list of MNMs and their efficiency in the confiscation of different HMs and dyes as well as their various SCs




Kinetic model

Isotherm model/Qm (mg.g−1 )



Magnetic Fucus vesiculosus (brown algae)

MB and crystal violet (CV)

5 and 3


LGR/577 and 1062


SDS-coated MNPs

Methyl violet (MV)





γ-Fe2 O3 –Al2 O3






Nanosized metal oxides—modified AC

Malachite Green (MG) and RhB

9.6 and 2.38


Koble-Corrigan/4.31 and 2.88 mmol g−1


Graphene oxide-mesoporous iron oxide nanohybrid (GO/ m-Fe3 O4 hybrid)

RhB and MB





Fe3 O4 /activated carbon

Bismarck brown (BB) 7




Magnetic NCs hydrogel (PVAcMAn/Fe3 O4 /Me)







Acid Yellow 42 2 (AY42) and Acid Red 213 (AR213)


LGR/62.36 and 77.99 62.36

Spontaneous and endothermic


Fe3 O4 @SiO2 @Kit-6/NH2

Sunset Yellow (SY), RhB, Ponceau 4R (P4R) and Brilliant Blue (BB)



LGR/8.41, 10.89, 6.26, 5.41 and 7.14



Zeolite-IO MNCs





Spontaneous and exothermic



RO 16





Fe3 O4 or γ -Fe2 O3 NPs


LGR/48.1 and 105.3

[137] 157


Applications of Magnetic Nanomaterials for Wastewater Treatment

Table 4 (continued)


Table 4 (continued) Nano-sorbents



Kinetic model

Isotherm model/Qm (mg.g−1 )



PANI/CeO2 (PANI/CeO2 -1 and PANI/CeO2 -5)

Remazol Red 133 (RB-133)



FRH/18.6 and 13.9

Spontaneous and endothermic



Naphthol green B dye 3 (NGB)



Spontaneous and endothermic


Bare and surfactant-functionalized CeO2 NPs

Methyl orange (MO), 5 victoria blue (VB), RhB 6G (RhB6G), direct red (DR), brilliant blue, (BB), (CR), fast green (FG), eriochrome black-T (EBT)


FRH/75112,4-171.3 (EBT)

Binary NCs (BNCs)




Spontaneous and endothermic







Spontaneous and endothermic




84.32 and 97.51


Acid-activated kaolinite clay (AAC)/TiO2

Mn2+ , Fe3+ , Cu2+ and – Pb2+


LGR/0.678, 3.989, 0.169, and 0.002

Spontaneous and endothermic


SiO2 –TiO2

Acid Yellow 219 (AY219)




CuO/TiO2 NCs





TiO2 /CS and TiO2 /CS-CMM Thymol violet (TV) NCs


U. O. Aigbe et al.





Kinetic model

Isotherm model/Qm (mg.g−1 )



γ-Al2 O3

Cr6+ , Pb2+ , Cd2+ and Ni2+

3 (Cr6+ and 5 (Pb2+ , Cd2+ and Ni2+ )

PSOR (Cr6+ , Pb2+ and Ni2+ ) and PFOR (Cd2+ )

LGR and FRH/13.3, 6, 1.1 and 0.33


Fe2 O3 /Al2 O3 microboxes (MBs)

Hg2+ , Cd2+ , Cu2+ , and Pb2+

7 (Hg2+ )

PFOR (Hg2+ )



Poly (Vinyl Alcohol)/Al2 O3 (Al2 O3 -PVA)





Al2 O3 /GO/HNT NCs

CR and MB

3 and 9


FRH and LGR/329.8 and 258.4

Spontaneous and exothermic


Fe3 O4 /MnO2

Cd2+ , Cu2+ , Pb2+ , and 6.3 Zn2+




Biochar-impregnated MnO2 NCs

Cu2+ and Zn2+


LGR/1,124 and 995

Spontaneous and endothermic


CeO2 NPs supported on CuFe2 O4 nanofibers

Pb2+ , Ni2+ , and V (V) 7 and 6


LGR–FRH/972.4, 686.1, – and 798.6



Pb2+ , Cd2+ , Zn2+ and Cu2+


LGR/490 (Pb(II))



Spontaneous and endothermic

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Table 4 (continued)



U. O. Aigbe et al. ◦

For considerable sorption to take place, the △G of the SP must be negative and it is defined by Eq. 1. ◦

△G = −RTlnK D


R, T and KD signify the gas constant (8.314*10–3 kJ.mol−1 K−1 ), the absolute temperature and the equilibrium constant which is provided by K D = Cqee . The △H and △S were evaluated utilizing the following association in Eqs. 2 and 3. Their values are estimated from the intercept and slope of the plot ln KD against 1/T [117]. △G = △H − T△S


△S △H − R RT


lnKD = ◦

Positive and negative values of △H signifies the endothermic and exothermic ◦ nature of the SP of contaminants to the MNMs. A positive △s values show enhanced unevenness/randomness across the interface of the solid solution during the SP, ◦ making slight structural changes to both sorbent and sorbate. While negative △s ◦ values signify a reduction in the irregularity of sorption. When △G is negative and positive, the SP is spontaneous or favourable and non-spontaneous or unfavourable [114]. As observed from Table 4, determined thermodynamical parameters show that the sorption of most pollutants (HMs and dyes) to the MNMs were spontaneous, endothermic and in some case exothermic.

7 Conclusions and Future Prospective The development of customized NPs with magnetic features as well as their high sorption ability present a new means to deal with effluent decontamination. Also, their functionalization has lately been assessed as a capable tool for the detection and decontamination of industrial wastewater. The confiscation of HMs and dyes was found to depend on the pH, sorbent dosage, initial contaminant concentration, contact time and temperature from the research reviewed. The optimum sequestration of various contaminants to MNMs was noticed in the range of pH 2–9.6. Equilibrium sorption data showed that the LGR and PSOR models generally described the SPs of various pollutants to different MNMs. Thermodynamically, the interaction of most pollutants and MNMs were found to be spontaneous, and endothermic or exothermic. The fabricated MNMs were found to be effective in the sequestration of pollutants from an aqueous-medium and should be applied in the treatment of real industrial wastewater. Nevertheless, before industrial use from a laboratory level, research on

Applications of Magnetic Nanomaterials for Wastewater Treatment


their general fabrication, with precise morphology, biocompatibility, stability and surface functionality optimization should be considered in the future.

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Magnetic Nanomaterials for Decontamination of Soil Onyedikachi Ubani, Sekomeng Johannes Modise, and Harrison Ifeanyichukwu Atagana

Abstract Several persistent organic and inorganic pollutants enter the environment accidentally or deliberately due to diverse advances in industrial activities, causing adverse alterations in the ecosystem and threatening human health. The quest for unique technologies to remediate environmental pollution is paramount. Consequently, nanotechnology, an evolving scientific approach, has been used in diverse fields, and nanoremediation (NNR) an engineered nanomaterial purposely for environmental remediation, proved effective, rapid, and efficient in the treatment of contaminated soil due to its diversity and versatility in applications. Thus, magnetic nanoparticles (MNPs) are superparamagnetic because of their nanoscale size, which has excellent potential in various applications. They have become an efficient tool for soil remediation due to their intrinsic qualities, providing target specificity and cost-effectiveness compared to conventional treatment methods. The techniques are essential to separate the polluted negligible particles from the residual materials in any soil remediation approach, thereby reducing the accretion of pollutants while controlling their spread from one medium to another. Hence, nanoremediation using MNPs is a new option that treats soils contaminated by organic, heavy metals (HMs) and metalloid pollution. Keywords Heavy metals · Magnetic nanoparticles · Nanoremediation · Soil contamination

O. Ubani (B) · S. J. Modise Department of Biotechnology and Chemistry, Vaal University of Technology, P. Bag x021, Vanderbijlpark 1900, South Africa e-mail: [email protected]; [email protected] H. I. Atagana Institute for Nanotechnology and Water Sustainability, College of Science, Engineering and Technology, University of South Africa, Florida Campus, Roodepoort 1709, South Africa © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 U. O. Aigbe et al. (eds.), Magnetic Nanomaterials, Engineering Materials,



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1 Introduction The rapid industrial development and suburbanization globally have caused a heavy compromise and contamination of soils. Soil pollution is due to the deliberate dumping, improper treatments, management and disposal of untreated toxic waste from different sources, including agricultural activities, into the soil [1, 2]. For instance, metals and persistent organic pollutants (POPs) are organic contaminants which threaten soil quality because they are toxic and accumulate in soil for a long period. They are pesticides, deliberate or accidental byproducts of industrial waste like polycyclic aromatic hydrocarbons (PAHs), HMs, polychlorinated biphenyls (PCBs) and many more (Fig. 1) [3]. They are one of the soil’s contaminants, which are non-biodegradable and persist in soil for a lengthy period from the point of entering into the soil. These pollutants are toxic and hazardous materials, and if not properly managed, they create significant adverse conditions and environmental concerns. These materials are harmful derivatives often produced by building sites, industries, farms, laboratories, garages, and various production and manufacturing plants, many of which end up in the soil. Due to their nature, their disposal is by specially approved amenities. Because their accumulation in soil (persistent toxic wastes) has adverse effects on the soil, affecting the soil layer strength in the topsoil, and consequently reducing the fertility and biological activity of the soil. Soil pollution threatens life on Earth by substantially causing various health problems with severe conditions such as kidney and liver damage, neuromuscular blockage, and several types of cancer (Fig. 2 as adopted and modified from [2, 4]). Therefore, searching for safe disposal or treatment of such complex pollutants generated by many industries entering the soil at concentrations high enough to endanger the environment has been challenging [5–7]. Because of the consequences of soil pollution on the ecosystem, research on innovative methods to treat or manage

Fig. 1 The sources of HMs pollution in soils

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Fig. 2 The sources of HMs in soil and their toxic consequences on humans

soil pollution and its hazardous impact on the environment is needed because the confiscation of contaminants from the soil should be linked with ecological remediation [8]. However, the remediation of polluted soils could be challenging because of the interfaces of contaminants, including variations in solubility, evolution, phylogenesis and bioavailability, contesting for adsorbents on the binding sites (Bss) and inhibition of microbial metabolism may cause synergetic and aggressive impacts on the remediation process [3]. In recent years, a branch of science, nanotechnology, has played a significant role in solving different environmental challenges. Nanotechnology in the environment has progressed impressively in biological, chemical, and physical remediation methods in treating polluted soil through nanoscale fragments to eradicate or diminish contaminants from soil [9]. Lately, the application of nanomaterials (nms) in soil remediation has drawn massive attention because of the superior reactivity, extraordinary surface-to-volume ratios, surface-functionalization, and physical properties modification like chemical composition, morphology, porosity, and size. These properties possessed by nms are helpful in their selectivity and efficiency in removing contaminants. The introduction of NPs in soil permits the clean-up of broad areas and minimizes costs and intervals because of the in situ application [1]. The core benefits of nms for soil remediation, particularly for general cleaning contaminated soils, are cheap cost and cleanup time interval, degradation of pollutants, needless disposal of polluted soil or transfer of the soil [8]. Nanoremediation applications are the use of combative NPs for the transformation and decontamination of pollutants. The primary functions of NPs in remediation are catalysis, chemical reduction, and sorption because NPs possess excellent surface area-to-mass ratios, diverse allocations of active sites (Ass), and increased sorption capacity [9]. Furthermore, NPs could disperse and enter the minute spaces in the subsurface, and NPs


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are versatile and can move long distances and accomplish more excellent spatial distribution [9]. Remarkably, small-sized NPs of 1–100 nm scale can be injected in small spaces and their activation with time enhances enzymatic activities. Thus, their advanced applications have led to various synthesized NPs, such as Fe-based in polluted soils [10]. An example is magnetite (Fe3 O4 ), an iron oxide (FeO) comprising iron in its bivalent or diatomic state, Fe(II), though, in this form, it is a mixed oxide containing Fe(III) and Fe(II) with an inverse spinel structure. In Fe3 O4 , FeO has been discovered to act as a catalyst that increases Fenton oxidation, that improves electron transfer in the degradation of organic pollutants, and then, an adsorbent (ADBs) with organic coatings, and stabilizer for surfactant foams [10]. Adsorbents are widely applied to treat HMs contamination due to their suitable fabrication, straightforward regeneration and excellent mechanical strength [11]. Recently, MNPs is known as higher adsorbents for eliminating polluting environmental composites. Nevertheless, its allured capacity is not the only specific reason for its usage. Their amazing surface charge and redox activity features are the conspicuous bases for their criterion of why they are preferred over other materials [12]. Magnetic separation is a remedy used by industries for HMs treatment, primarily for separating pollutants from soil to enable the reduced volume of waste or polluted soil. Even though magnetic separation techniques have shown promising effects, there are still commercial limits: the application of surface-modified MNPs raises the rate of partitioning procedure as a result of its complicated synthesis via the coating of functional materials on bare Fe3 O4 NPs [13].

2 Magnetic FeO NPs (MFeONPs) Synthesis MFeONPs have been described in many reports with versatile compositions and levels. The most outstanding quality of MFeONPs is synthesized by adaptable synthetic methodologies, including thermal breakdown, coprecipitation, micelle creation, magmatic and beam pyrolysis procedures (Fig. 3) [14, 15].

2.1 Biological Synthesis Green chemistry in nanotechnology is the manipulation of chemicals to reduce or remove toxic materials from the environment, which has drawn the attention of many scientists worldwide. Biologically, plant-mediated metallic nms are syntheses using different plant parts such as tissue, extracts, and exudates. These biological nms are environmentally friendly, safe and nontoxic in applications because they comprise reducing agents such as Cit A, Vit C (AA), C15 H10 O2 , and raw enzymes such as DHs, SDRs and EESs. These components play a vital part in the biological production of

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Fig. 3 The synthesis of MNPs with different methods. Diverse synthetic techniques have been used for MNPs of preferred sizes, morphology, stability, and biocompatibility; most techniques in synthesizing MNPs comprise the ball milling method, co-precipitation, thermal decomposition, hydrothermal, microemulsion, sol–gel method, and biological method. Adapted from Ali et al. [15]. Copyright, Frontiers publishers, 2019. Reprinted with permission from Frontiers publishers from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY)

NPs. The use of leaf extracts has been swift, nontoxic, and facile in synthesizing FeO magnetic NPs. An example is the Carob leaf extract in one reaction with iron(III): iron(II) and NaOH solutions [9]. This process takes place at a lower-temperature level in a onevessel reaction via a typical radius of the monodispersed NPs (4–8 nm) covered in R − COOH of Amide-I and II chains of the amino acid in the extract [14]. The drawback in the bio-synthesis of NPs using plant parts is the production of small amounts of secreted proteins by plants leading to a reduced synthesis rate. Because the biological products of NPs are an absolutely novel methodology and are emerging, there are definite drawbacks related to it. For instance, plants yield low amounts of secreted proteins leading to a reduced synthesis level. Another disadvantage is that all plants cannot be used for nanoparticle synthesis [14]. Interestingly, the capability of MNPs to remediate pollutants in soils has been tested, predominantly using a mixture of the starch-stabilized MNPs with amended


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soil and actual contaminated soil, which showed that the greater the dosage, the better the immobilization of the pollutant [14]. Previously, it was applied to decontaminate Cs-contaminated very small particles from bigger soil particles and accomplished significant separation. Nano-Fe/Ca/CaO/[PO4 ] compounds have been applied to immobilize Cs-sorbed clay and were separated from contaminated soil by a modest pulverized technique in dry conditions: Eighty percent of the harmful Cs made up 27 wt.% magnetic soil particles [13]. An experiment also confirmed that cationic polymer-coated MNPs could separate Cs-polluted clay selectively from polluted soil. The smaller particles were separated successfully into magnetic portions using polyethyleneimine-coated MNPs [13]. Several NMs have been employed to remediate soil and groundwater, mainly MeOx, Z-NZVI, enzymes, CNTs and fibres, TiO2 , and noble metals. However, the commonly used nanomaterial for the remediation of soil and groundwater is zero-valent iron (nZVI) because it is regarded as the best electron donor and extremely reactive [9].

2.2 Zero-Valent Iron NPs (ZVI-NPs) Several studies were centred on removing pollutants by zero-valent iron (ZVI) because of its naturally nontoxic, sufficient, cheaper, simplicity in synthesis, and bioavailability. Pollutants were removed by a mechanism involving the transference of electrons from ZVI to pollutants, converting pollutants to nontoxic or less toxic species. Also, Zero-valent iron could be used to degrade and oxidize some organic compounds with DO-producing H2 O2 . Then, H2 O2 could be condensed to water by the transportation of two-electron from ZVI. Thus, this Fenton reaction takes place via blending iron (II) and H2 O2 , producing OH. which has the strong dissolving ability for some organic compounds. Metallic iron NPs have the potential for magnets, and their use is anticipated to stimulate the magnetic reclamation steps. N-ZVI shows tremendous surface activity. As such, ZVI NPs are widely used to remove contaminants (HMs), by creating an oxidation state. The hydrogen produced during the oxidation state on the ZVI NPs surface effectively eliminates pollutants. Furthermore, various active sites on the surface of ZVI are helpful for the removal of contaminants [11]. However, the NPs dimension and the compact condition of ZVI-NPs could promptly interact with environmental media, which causes agglomerates in the synthesis process, decreasing the reactivity of ZVI-NPs, causing slow movement of ZVI-NPs to the pollutants, which limits the comprehensive usage of ZVI-NPs. Therefore, to decrease ZVI-NPs aggregation, it is usually mixed with a coat such as Gr, Si, clay, or a membrane [11]. Furthermore, ZVI-NPs as a reducing material gained attention because of their outstanding benefits like specific large surface area, inexpensive, and amazing reactivity with HMs. An example is an improved removal of Cr+6 with amino-functionalized vermiculite-supported ZVI-NPs (AVT-ZVI-NPs), which was stable [11].

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2.3 FeO(s) FeO NPs have shown their sorption activities because of their specific large surface area, permeability configuration, and strong magnetic reaction attributed to their excellent sorption capacity. They have been in different structures, such as hematite (a-Fe2 O3 ), Fe3 O4 , and maghemite (c- Fe2 O3 ). The magnetic effects of a-Fe2 O3 are determined by many factors like crystallinity, sub-particle structure, particle size, exchange interfaces, and cation doping. Although the photocatalytic activity of aFe2 O3 is limited due to its lesser separation efficiency and poor conductivity, it mixes with diverse semiconductor constituents to create a heterostructure. For instance, the synthesis of a-Fe2 O3 with graphitic carbon nitride-based Z-scheme heterojunction via simple solid condition reactions improved the efficiency of photocatalytic degradation of organic pollutants/dyes and HMs ions such as Cr (VI) and Cd2+ and Cu2+ with elevated pH. Once more, the synthesis of a-Fe2 O3 and aluminium oxide composites has shown a large specific area, sorption effect and permeable configuration of a-Fe2 O3 and aluminium oxide with extraordinary removal proficiency on Hg2+ , Cd2+ , Cu2+ , and Pb2+ cations [11].

2.4 Fe3 O4 Fe3 O4 comprise Fe2+ and Fe3+ ions. The adsorbent effect of Fe3 O4 is determined by its effective surfaces and morphological features. The degradation efficiency increased by an enhanced catalyst dosage because of the increased surface area of the catalyst, which improved the Adpt of photons. Fe3 O4 can remove HMs from the environment example is the synthesis of CMC-immobilized Fe3 O4 NPs (CMC-Fe3 O4 ), which displayed better sorption capability for Pb+2 and HMs removals like Cd, Cu, Fe, Zn, and Ni than other pure Fe3 O4 NPs [11].

2.5 c-Fe2 O3 c-Fe2 O3 NPs have large chemical stability devoid of any decrease reaction due to their magnetization saturation, facilitating the proficient separation of contaminants from the environment. In contrast, it is commonly utilized because of its nontoxicity and cheaper synthesis than most materials [10]. Several pollutants could be removed using c-Fe2 O3 polymers by electrostatic interactions, such as the elimination of Cr+6 and Cu+2 by PPY/c-Fe2 O3 and PANI/c-Fe2 O3 . Thus, c-Fe2 O3 NPs could be better adsorbents for arsenic(V) As5+ than Fe3 O4 because concrete/c-Fe2 O3 nanocomposite (CM nano) has been shown to be an excellent adsorbent for the decontamination of As5+ [11].


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2.6 Spinel Ferrites and Their Composites Spinel ferrites and their composites have been applied in the decontamination of polluted environments because of their magnetic behaviour, stability, and biocompatibility. However, their catalytic reaction is determined by their polymerization process, which is the adjustment of the crystalline, crystallite size, and particular surface areas by several calcining temperatures and diverse pH values. The spinel ferrites removed aromatic nitro compounds from the environment because they are not complex but simply synthesized, including their high resistance to strong acidic and basic conditions. The magnetic reclamation effect of MFe2 O4 (M=Zn, Co, Mn) spinel ferrite NPs was effective for the decontamination of nitroarenes composites because they possess huge pore capacity area as an advantage to the other ferrites NPs. The spinel ferrite configuration shows greater ferromagnetism, nontoxic effects, and outstanding photochemical stability; thus, their application is like a catalyst to remove soil pollutants. Furthermore, AgI/CuFe2 O4 composite revealed excellent magnetization and cycling performance separation from pollutant mixture because of their distinctive magnetic effects, stability, and sustainability. Therefore, the recyclable heterojunction composites combining the magnetic spinel ferrites and photocatalysts capability is a promising approach to removing contaminants [11]. On the other hand, carbon materials such as graphene (Gr), chitosan (CH or CS) and MWCNTs drew substantial awareness because of their distinctive configuration and effects. They are viable in the elimination of HMs and radioisotopes (RxList). However, MWCNTs are incredibly hydrophobic and aggregate in solution because of the reaction that occurs in them, which could hamper the compelling sorption efficacy and drop the sorption effects; thus, to improve their sorption efficiency, which should occur in a combination of magnetic ADBs such as the spinel ferrites. In addition, the sorption approach’s mechanism and kinetics are determined by features like superficial configuration, magnetic effects of the ADBs and treatment parameters which may include pH, adsorbent concentration, contamination period, temperature, and pollutant concentration. However, magnetic adsorbents reportedly encountered several challenges requiring further research and development to enable multiple pollutant solutions [11].

3 The Fate of NPs in Soil The use of NPs for decontaminating pollutants from the soil may lead to their accumulation or increased constituent concentration in the soil, thereby altering the soil’s properties. The addition of NPs in soils can adjust the soil pH, and pH is an essential parameter that regulates soil nutrient availability, microbial dynamics, general soil health, and plant growth and development. When soil pH is altered or adjusted due to

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the presence of NPs, it could cause adverse effects on soil microorganisms and nematodes because NPs can attack mycelium and significantly destroy the functioning of microbial cells. The adverse effects caused by NPs in soil could be attributed to their concentration and type, soil type, and the enzymatic activity of the soil. For instance, higher concentrations of NPs in soil may lower dehydrogenase activity. As such, the equilibrium of the soil nutrient and fertility levels is disrupted. The sorption of NPs in soil could be mostly by surface complexation, hydrophobic partitioning, and ion exchange, and the colloid-facilitated transference of pollutants also follows these procedures [10]. The elimination efficacy increases as the concentration of nano adsorbents increases; this is assisted by the availability and functionality of active surface sites, viable attraction, and extent of surface charge (positively or negatively charged) on NPs for the sorption of metal ions, thereby developing chelate complexes for pH. This occurs because the removal of metal ions improves with a higher pH level of the solution resulting in the complete elimination of metal ions [13, 16]. Therefore, nanoscale particles significantly impact metal transference, maybe slowly trapped in soil or speeding up their movement. As such, the application of NPs in decontaminated soil should be deliberate and tailored to encourage its viable applications because the removal efficacy of metal ions from the soil is tremendously reliant on the pH of the solution [16, 17].

4 Decontamination of Soils Using NPs Most soils are contaminated by organic and inorganic pollutants at higher concentrations; this type of soil pollution becomes a challenge in terms of making the right choice of remediation technologies suitable for removing the contaminants. The typology of pollutants and soil biogeochemical properties adds to the complexity of the challenge because either of them impacts or limits the removal of soil contaminants. In soil, these contaminants could be in particulate forms, adsorbed, absorbed, or disintegrate in soil pores. Each behaves differently because of soil parameters such as pH, OMC, and CMC which impact their mobility and availability in soil [18]. For instance, As, in its oxidized state, particularly at acid-neutral pH, adsorbed to Fe and Al oxides, to a reduced scale. In Na-contaminated soils, As becomes mobile and is free from the compact phase to soil dissipation, like AsO4 −3 . In plummeting surroundings, As also takes the form of an AsO3 , which could be absorbed by the clay segment via added energy than the AsO4 −3 . Indeed, As+3 are more toxic than As+5 because it forms more stable multiplexes with the Sulfhydryl groups (SH) enzymes. The oxidative ability of MnO2 is adequate to dissolve the AsO3 to AsO4 −3 . Then, regarding Cr, it is established that in the normal state, particularly in tri- and pentavalent forms. The trivalent form produces stable multiplexes with organic and inorganic ligands comprising O2 or N. In soil, these metals penetrate quite a few depths. Overall, typical soil environments favour the Cr+3 form, in which residues are fixed, and absorb on the surface of O−2 and SiO3 2− , creating stable links straight at acidic pH. At pH beyond 5, Cr(OH)3 is discharged as an OH¯. In alkaline pH media,


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Cr+3 dissolved into CrO4 2 − , which is a poisonous formation of Cr. The presence of MnO favours this oxidation. The Cr+5 type is extra motile than Cr+3 , particularly in organic matter (OM). The OM performs as a reducing agent, and, furthermore, it is complex, withholding the production of Cr+3 in the process [18]. Also, PAHs are oily wastes that are substantial sources of organic hydrocarbon pollutants in the environment, like oil-derived fuels [18]. Polycyclic aromatic hydrocarbon (PAH) gained significant attention in ecological studies due to its high resonance energies and dense clouds of pi electrons of the benzene rings, making them POPs, recalcitrant to degrade in the environment [18]. The behaviour of PAHs is determined by their specific environmental exposure. They could be absorbed into the soil’s OM; and their bioavailability is limited, making them less susceptible to remediation. Numerous procedures have been applied, with different outcomes, trying to degrade these recalcitrant complexes; such procedures were chemical degradation, biodegradation, phytodegradation and a combination of degrading techniques. The success achieved depends on the environmental factors, the microbial populations and class, and the kind and pollutants configuration [8]. Thus, the use of nZVI for the remediation of polluted soils is motivated by electron transfer and sorption as well as fixation effects. Such that nZVI are more active in the immobilization of HMs and metalloids in soils. The PCBs degradation in polluted soil was tested using nZVI; however, it was noticed that soil properties affected the nanoparticle efficiency for PCBs degradation, but at three hundred degrees Celsius in the air combining FeO and V2 O5 /TiO2, nZVI acted as a catalyst for remediating PCB contaminated soils. Furthermore, nZVI-Pd showed positive results in degrading PCBs contaminated in soil; again, it was noticed that soil properties affected the nanoparticle efficiency for PCBs degradation. Then, applying MFeO-NPs, like nFe3 O4 , in soil amended with As and PAH yielded positive results in pollutant immobilization and reduced soil toxicity. This may be because of its elevated sorption abilities and magnetic effects that improved the decontamination from the medium by magnetic energy. Then, the application of nFe3 O4 as a catalyst in a Fenton procedure was mixed with a dissolving agent, such as H2 O2 or K2 S2 O8 , which degraded PCBs in sand amended PCBs at > 69%, though, in naturally polluted soil, degradation capacity with the same treatment was limited to 7–8%. Once more, iron NPs such as nZVI, nZVI-Pd and nFe3 O4 were evaluated to remediate industrial Cr and PCBs contaminated soils, which aimed at comparing the effectiveness of Fe-NPs for the reclamation of soil polluted with Cr and PCBs, indicating positive degradation [3].

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4.1 PAH Remediation Using Activated Carbon-Based Nanomaterial Activated carbon-based nms are novel NPs because of their properties and applicability. They have been used in PAHs remediation, which included fullerenes, SWCNTs, MWCNTs, as well as graphitic materials. Carbon nanotubes (CNTs) drew massive attention because of their distinguished structures, like advanced biological strength, heat resistance, sorption ability, and stable pH ranges. They are the utmost favourable NMs for remediating contaminants as adsorbents. Their large surfaceactive site-to-capacity ratio and controlled pore size dispersal of customary adsorbents make them unique for remediation. However, the challenge in using CNTs is the option of accumulation, a drawback in the decontamination procedure, but the solution is integrating a functional group [19].

4.2 MNPs MNPs were applied to decontaminate As -polluted soil. magNPs reduced As concentration in an extractable stage because of the sorption of contaminants onto MNPs [20]. The capability of magNPs (ZVI NPs and Fe/Cu NPs) to fixate As in soil and decrease its movement via immobilization was established. However, the sorption of As is influenced by soil pH because alkalinity promotes condensation of As+5 and Fe(OH)2 and promotes As immobilization [21]. Thus, NPs of binary oxides (Fe–Mn binary oxide NPs) were also prepared and applied to immobilize As in soil as an in-situ method [22, 23]. Metal NPs have been used to decontaminate and restrain pollutants in soil, and metal NPs (SiO2 NPs) reduced the concentrations of Zn, Ni, as well as Cd to a reasonable extent [24]. Notably, NPs composites such as biochar with iron phosphate NPs and sodium carboxymethyl cellulose improved immobilization of Cd in soil via reduced bioaccessibility and filtration, suggesting the augment of NPs composites (nGoethite and nZVI) for the remediation of contaminated soils [25]. Furthermore, applying the NPs composites (nZVI) in soil remediation did not alter the soil parameters at a lower dosage; instead, the reduction in soil phytotoxicity occurred, but the soil phytotoxicity rose as the EC of the soil rose at a higher dosage. The application of MNPs in remediating polluted soils is viable because of their simplistic partitions via their magnet and distinctive metal-ion ADPT. Nevertheless, eliminating non-magnetic HMs such as Cd and Pb by chelation as well as separation by magnetic force using MNPs (core–shell Fe3 O4 @SiO2 NPs and iminodiacetic acid chelators) from contaminated soil was successful. However, the application altered only the soil’s organic content and not the soil’s chemical composition [9, 26].


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5 Environmental Effect of Magnetic NMs in Soil Remediation The application of NMs in soil remediation has been successful, but NMs may have a harmful impact on humans and the environment. The route and features prompting ecological toxicity are complex. Thus, lots of factors may influence the impact of synthesized-NPs on organisms, such as dissolution perspective, particle surface effects, accumulation potential, contact with environmental materials, and physiological, biological, and microbial behaviour in contact with NPs [9]. Exposure to nms impacts negatively the environment and humans, like FeO-NPs with mutagenic effects because they could destroy organisms’ growth capacity or replicate [27]. The impact of nZVI in ranges of 1 to 20 mg L−1 in concentration on soil microbial mode was examined in sandy-loam (SLS) and clay-loam (CLS) soils. It indicated that soil type has affected the amount of possible toxic effects on soil microbial populations by nZVI. The effect could be attributed to the mass organic content (OC) in CLS, which acted as a defensive mediator in addition to nZVI to the soil, thus, making nZVI inactive by hindering interface with soil microbial cells. During the remediation of SLS using nZVI, microbial biomass and aryl-sulphatase activity, heterogeneity, and richness in the soils were adversely altered, and there was no exact concentration responsible for the influence on the soil. This implies that more research may be necessary with a variety of soil types and proprieties for a better understanding of the influence of soil properties and type on the effect of nZVI on soil microbial populations. This is because composites of nZVI have shown different effects in different studies, which may be attributed to the colloidal stability of nZVI properties and dosage, soil type and properties/parameters, contaminants type and their concentration and soil bacteria communities [9, 28–39]. In addition, the chemical conversions of nms in the environment are tremendously complex, which include the reduction, oxidation, dissolution, sulfidation, biodegradation, ADPT of macromolecules, and degradation of the surface-coated materials [34–36]. Nevertheless, the application of nZVI in the remediation of contaminated soils is encouraged as a viable nanoremediation devoid of ecotoxicity effects [40]. Though, anecdotal evidence recommends that the reactivity of nZVI in contaminated soil could be influenced by combinations of complex elements, such as contaminant types, nZVI properties, the soil geochemical conditions (pH, EC, temperature, NOM, moisture, DO), soil phytotoxicity and the ageing soils [10, 35, 41, 42]. However, there are several advantages to applying nanoremediation, such as reduced temperature changes, extra tunable pore dimension, smaller inter-particle distribution, and different surface interfaces [43, 44]. Remarkably, NMs retain larger surface spaces due to their distinctive features and radical sorption sites, leading to their exceptional absorbent [45]. Therefore, NMs have been considered a promising technology to remediate soils polluted with hazardous chemicals such as chlorinated organic solvents, organochlorine pesticides, HMs, PCBs and PAHs. NNR methods have been classified as economical, eco-friendly, viable, and rapid remediation techniques;

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these make NPs and NMs outstanding in the reduction/oxidation, catalytic degradation, precipitation, and co-precipitation of chemicals, as well as catalysis in degradation that could alleviate the absorption/sorption of targeted pollutants in soil [35, 44, 46, 47]. Furthermore, the latest finding on the relations between photo-catalysts and microbes has unlocked a broad path for long-term environmental pollution remediation, focusing on the long-term improvement of photo-catalysts [44, 48].

6 Conclusions Magnetic nms for the decontamination of co-contaminated soil focus on the transformation and detoxification of the contaminated soils. Nevertheless, the components and varying properties of the soil environment impact Magnetic nanomaterial’s performance physically, chemically and biologically, which leads to the harmful effect of Magnetic nms on organisms that induce contrary effects on the soil bioremediation process. Coating magnetic nms could reduce the toxic impact on soil microorganisms. The key benefits of applying NMs in soil remediation are a decrease in cleaning period and total expenses, reduced contaminants to virtually nothing in sites, thus, needless disposal of polluted soil. The extensive application of NMs in environmental remediation is because of their pronounced reactivity and extraordinary capacity to immobilize HMs such as Cd, Ni, and Pb. It has been revealed that using nZVI to immobilize As and Cr in the soil could efficiently reduce the concentration of the pollutants. Granting that the diffusion in concentrations of analytes and pollutants suggests that the stability of the treatment and relations between HMs and the soil components have to be examined. Several studies revealed that magnetic separation by uncoated Fe3 O4 NPs in an acidic condition effectively eliminates polluted soil. This is because a decrease in pH raises the positive charge on the surfaces of MNPs, which causes a strong bond with negatively charged clay particles because of their ferromagnetic attraction. Considerations of dosages during the applications of NPs (below or above 1%) via sorption processes are essential in soil remediation because dosages of NPs enable complete immobilization of pollutants concentration such as As, TPH and PAHs in the soil. Soil remediation with MNPs is viable because of its exceptional separation mechanism. However, the combination of NNR and other remediation technologies seems to be better for soil remediation because the combination procedure improves sustainable remediation practices for green environmental protection practices. For instance, using the magnetic effects of the NPs in combination with other remediation technologies could efficiently help improve pollutants adsorbed on the NP surfaces. As such leads to increased pollutant immobilization and a decrease in soil toxicity with suitable effects of the magnetic NPs such as size, sorption mechanisms, and magnetism. Though numerous remarkable achievements have been recorded with magnetic NPs for the remediation of contaminated soil, thus, studies regarding magnetic NPs or in combination with other bioremediation technologies are essential to improve the remediation systems.


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Magnetic Nanomaterials-Based Sensors for the Detection and Monitoring of Toxic Gases Joseph Onyeka Emegha, Timothy Imanobe Oliomogbe, and Adeoye Victor Babalola

Abstract Magnetic nanomaterials (MNMs)-based sensors have found a growing interest in the detection and monitoring of toxic gases. Since the development of MNM-based sensors, magnetic materials have become an integral part of electronic sensor fabrications. The MNMs are easily embedded into the transducer materials, and their interaction with the surface is easily recognized by an external magnetic field. The chapter focuses on the various MNM-based sensors, considering their principles, types, applications, strengths, and demerits. The discussed MNM-based sensors are electrochemical, optical, piezoelectric and magnetic. An overview of the recent literature is given, and their various applications are also presented therein. Keywords Electrochemical · Magnetic nanomaterials · Sensors · Transducers · Piezoelectric

1 Introduction Nanotechnology is one of the newly emerged research trends in science and technology that is based on material science, quantum mechanics, microelectronics, computer science and molecular biology [1–5]. The term “nanotechnology” refers to a scientific way of synthesizing new materials on nanoscale levels (1–100 nm) [1, 5]. On the other hand, nanomaterials (NMs) describe generally materials which are produced by nanotechnology or materials that possess a single unit in dimension measuring one to one-hundredth nanometers [3]. NMs have remarkable advantages over non-NMs or traditional materials in their physical and chemical characteristics due to the quantum size effect [6–8]. Besides, features such as small sizes and wide surface areas will essentially improve the functionality of NMs greatly [2, 5]. NMs J. O. Emegha (B) · T. I. Oliomogbe College of Natural and Applied Sciences, Novena University, Ogume, Delta State, Nigeria e-mail: [email protected] A. V. Babalola Nile University of Nigeria, Research and Institution Area, Jabi, Abuja, FCT, Nigeria © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 U. O. Aigbe et al. (eds.), Magnetic Nanomaterials, Engineering Materials,



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can appear naturally, or be purposely developed through engineering to carry out certain tasks [9]. It has numerous uses in a wide range of industries, including agriculture, medicine, transportation, and manufacturing extremely durable materials with high mechanical qualities [8, 10]. On the other hand, magnetic nanomaterials (MNMs) are groups of NMs that could be influenced via incident magnetic fields. The magnetic materials (Fe, Co and Ni) and the chemical components with functionality are usually two components of such material [1–3, 7]. Over the years, magnetic and superparamagnetic materials have been employed for a range of industrial uses in treatments like hyperthermia, magnetic resonance imaging and gas monitoring [7, 11]. The application of their various properties (chemical, electrical, thermal and magnetic) in various analytical processes of detection and chromatographic processes helps in the improvement and advancement of new diagnostic approaches with excellent precision, improved extraction recoveries, selectivity and overall detection speed [7, 11]. The fabrication of these nano-materials requires the application of various (metallic) magnetic materials such as iron (Fe), nickel (Ni), and cobalt (Co), as well as their various derived complexes [12]. From these metallic-magnetic materials, iron oxides, (ferric oxide and ferrous oxides) and their various ferrite derivatives (Cobalt Iron Oxide and Manganese Ferrite) are majorly employed in the fabrication of MNMs. This is suitably due to their excellent chemical properties, comparatively high magnetic moments, and ease in the preparation process when weighed against metallic alloys, such as Iron–platinum, Ni, Co and Manganese oxide [7, 13]. Usually, iron (Fe) oxides easily decompose under acidic conditions in addition to degrading in organic compounds [7]. It also effortlessly reacts with oxygen and, thus, modifies the functionalities of the material surface characteristics. [14]. These functionalities of the fabricated MNMs surface introduce various physic-chemical properties to the fabricated materials and improve the analytical abilities of the materials [14, 15]. MNM exhibits beneficial characteristics when compared to traditional materials or non-MNMs. Such characteristics like high surface area and possible functionalization or modifications for improved specificity, adsorption efficiency as well as ease of separation [7]. Additionally, MNMs are usually reusable/recyclable and cost-effective. Notwithstanding their countless merits, MNMs have some limitations. One of such limitations is the superparamagnetic or ferromagnetic properties which cause a reduction in their intrinsic magnetism due to agglomeration and aggregation in media [7]. This abnormality is overcome by modifying the MNMs with different materials. Such modification or functionalization could improve the rate of electron transfer within MNMs due to their conductivity. Other limitations of MNMs include ease of oxidation and the formation of hydrated oxides in an acidic environment [7]. These limitations of MNMs at high temperatures could reduce the accuracy or precision of the analysis [7].

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2 Magnetic Nanomaterials-Based Sensors Generally, sensors are machines or subsystems that detect changes within the surroundings and launch the signals into a computing workstation. In another word, sensors are devices or modules that generate a signal (output) to sense a physical phenomenon [16, 17]. Sensors are constantly used with an electronic machine or a computer. They have been greatly employed in the detection of toxic and damaging gases as well as for natural gas leakage [1]. Remarkable improvement has been recorded in the accuracy and sensitivity when determining the definite nature of gas due to the change from single metallic oxide to combined metal oxide [16– 18]. Various sensors are widely applied in our everyday activities [1, 16]. These applications include robotics, medicine, machinery, aerospace, cars, and many other facets of our everyday life. Other sensors determine the physio-chemical properties of materials, including, vibrational, optical and electro-chemical sensors for various monitoring purposes [17, 19]. The improvement of electronic devices (sensors) in recent times has brought about integration as well as miniaturization and microminiaturization of devices [2]. NMs are increasingly significant to the development of gas-sensors. Various benefits are derived, in terms of analytical figures of merit recognized [1, 2]. Such benefits include a short boundary of detection, improved sensitivity, and a reduced phase of analysis than traditional materials [1, 20]. Since MNM-based sensors are specific in function, it is imperative to note that a particular gas detector cannot detect every kind of noxious gas. They are manufactured to detect some low levels of oxygen which is crucial for industrial gas detection and sequentially to prevent fire outburst accidents [16–19]. The specific sensor would simply detect the exact gases for which it is proposed. Though each sensor comes with capabilities and limitations, one has to be careful when selecting a particular sensor for a specific application [16]. The following functional requirements should be considered when choosing any MNM-based sensor: high sensitivity, reproducibility, specificity, response linearity, stability as well as short response and recovery time [16, 17]. At room temperature, the development of reliable and lowcost sensing mechanisms for the detection of gases, has continued to pose a significant challenge to the technological and scientific world [17]. However, different MNMbased sensors could be grouped according to their detection methods. These sensing methods include diverse variations in optical, electrical, acoustic, calorimetric and chromatographic properties [1, 16–19]. Gas interaction usually occurs as soon as the surface of a sensing material is exposed to the environment, and, thus changes the main physical parameters of work function, conductivity and permittivity, as indicated in Fig. 1. An important element in sensor structure, the transducer, is responsible for the conversion of physical parameters from one form to another. Hence, in an electrically transduced sensor (chemical) where the gas particles relate to the sensing material, the interactions define the nature (stability, sensitivity as well as biocompatibility) of the sensing devices [17, 21]. The sensing material should be modelled in a way to have a wide surface for interaction with the related gas particles and, efficiently convert these required actions into


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Fig. 1 The detection method of sensing materials as adapted by Nikolic et al. [17]; Copyright, MDPI publishers, 2019. Reprinted with permission from MDPI publishers from open-access articles distributed under the terms of the Creative Commons Attribution License (CC BY)

measurable information. Additionally, the sensing material should exhibit suitable properties for easy processing of signals [6, 22]. By and large, sensors are being used to measure harmful gases as a result of technological and monitoring advancements [1, 2]. Sensor systems have a significant advantage over conventional sampling and analysis approaches for measuring harmful gasses accurately. The majority of these devices can be generically categorized into (1) electrochemical sensors, (2) optical, (3) piezoelectric sensors based on piezoelectric materials, and (4) magnetic sensors. MNM based-sensors are sensors that have at least one nano-material sensing dimension that is no larger than 100 nm. The MNM based sensors are essential in the field of nanotechnology because they can (a) monitor physical and chemical processes in hard-to-reach areas, (b) detect biochemical in cellular organelles, and (c) quantify micro particles in the environment [16, 17]. The major application of MNM based sensors in the detection of hazardous gases have been elaborately presented in the 2019 review article [16], which gives the hazardous gases to include acetylene (C2 H2 ), carbon monoxide (CO), carbon dioxide (CO2 ), Hydrogen (H2 ), hydrogen sulphide (H2 S), nitrogen monoxide (NO), nitrogen dioxide (NO2 ), chlorine (Cl2 ) as well as ammonia (NH3 ), and the various MNM-based sensors employed. Subsequently, the recent progress in this area is a comprehensive analysis of the various MNM-based sensors (electrochemical, optical, piezoelectric and magnetic) types, transducers and analytes types, their detection ranges and limits as well as their analytical figure of merits and applications [1, 2]. Recipes for these studies exemplified the applications of the MNM based sensors and their mode of operation in detecting hazardous gases. In

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this chapter, emphasis is placed on the overview of the different MNM-based sensors for the detection and monitoring of toxic gases.

3 Electrochemical Sensing Devices Electrochemical sensors are sensors that can provide accurate and timely information about the structure of a system by merging an electronically specific layer (the acknowledgement component) with an electrochemical transducer [19, 23]. Modern electrochemical sensors use a variety of features to distinguish between different limits, whether they are physical, chemical, or natural boundaries, in our everyday lives [2, 20]. They are well-established and reliable tools for obtaining constant cycle control messages through on-the-spot predictions of compound structure. The mid1950s saw the commencement of electrochemical detecting innovation [18, 23–26]. The most common approach for detecting oxygen and dangerous gases, such as carbon monoxide and hydrogen sulfide, is being used today [19, 26]. This method is not used to calculate flammable gases; however, it is the greatest option overall for monitoring ecological toxic gases. For on-site monitoring of priority pollutants in addition to addressing other environmental needs, electrochemical sensors and detectors are particularly convincing [16]. Many of the parameters for on-site environmental analysis’s needs are met by such devices. They feature constructed sensitivity to and selection against electro active species, are quick and precise, small, transportable, and affordable [1–3, 19]. Decentralized clinical analysis has already been greatly impacted by such capabilities. Broad electrochemical sensor applications for pollution management are still in their infancy, despite their enormous promise for environmental monitoring [1, 8, 27, 28]. In electrochemical sensors, the target analyte and the recognition layer interact to produce an electrical signal that contains analytical information [28]. Environmental monitoring can be done using a variety of electrochemical instruments (a subject on the sensitivity needs and the make-up of the analyte). The bulk of these procedures can be divided into two groups: amperometric and potentiometric sensors [26–28]. The foundation of amperometric sensors processes is based on the detection of biochemical recognition methods of electro active species [28]. The working electrode’s potential is fixed (relative to a reference electrode) during the signal transduction process, and the current is monitored as a function of time. The electro active species’ response to transfer electrons works as a result of the applied voltage [19, 26, 28]. The L.C. Clark oxygen cathode was the first amperometric sensor [28]. The oxygen that enters the framework via a gas-porous layer is condensed to water on an honorable metal-cathode. The composition of the working anode has a significant impact on the yield of amperometric sensors. The calculation of the current delivered by an anode surface enzymatic or bio affinity response with a constant working voltage similar to the reference terminal is what drives the amperometric sensor standard [27, 28].


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In potentiometric sensors, the whole detection process is turned into a potential signal that is logarithmically proportional to the various activities (concentrations) of species generated in the process [1, 2, 28]. This potential signal is then used to generate the analytical information. Ion selective electrodes are used in these devices to capture the potential signal. The electrode’s tip is equipped with a perm selective ion-conductive membrane that is intended to produce a potential signal that is largely caused by the target ion. Potentiometric sensors provide a high degree of selectivity, are easy to use, and are inexpensive, making them particularly appealing for field operations. However, they are frequently slower and less sensitive than their amperometric counterparts. Potentiometric instruments have historically been more extensively utilized, but as amperometric probe research grows, this balance should eventually shift [27, 28].

3.1 Principle of Electrochemical Sensor Electrochemical sensors are controlled by introducing the target gas into the sensor, which results in the production of an electrical signal corresponding to the convergence of the gas. In exchange, the sensing electrode oxidizes or reduces the diffused gas [28]. A typical electrochemical sensor consists of a counter terminal separated from the detecting cathode (or working anode) by a thin layer of electrolyte (Fig. 2 as adapted from [27, 29]). This technique allows a suitable quantity of gas to react to the detecting anode and generate an appropriate electrical indication. The gas joins at the exterior of the detecting cathode with either an oxidation or a decrease instrument after diffusing through the blockage. Exceptionally well-planned cathode materials for the target gas stimulate these reactions. When a resistor is connected over the terminals of the anode and cathode, a current proportional to the gas fixation flows between them, and the current can be computed in order to calculate the centralization of the gas [26–29]. Due to the simultaneous creation of a current, the electrochemical sensor is sometimes referred to as a small power device or simply an amperometric gas sensor [27–30]. The maintenance of constant and reliable potential is crucial for detecting anode for a sensor with an external driving voltage. The detecting terminal potential fluctuates because of the constant electrochemical reaction that takes place on the anode surface. It results in deteriorating sensor performance over time. In order to support the sensor’s effectiveness, a reference anode is included. Within the electrolyte, this reference anode is located close to the detecting cathode [26, 31]. When a constant voltage is connected to the detecting terminal, the estimation of this constant voltage at the detecting terminal is maintained at the reference anode. Thus, allowing zero current flows from or to the reference terminal. The particles (gas) react at the detecting anode, and the current flows are calculated between the detecting and the counter terminal, and the grouping of gas is typically easily recognized [29]. When the voltage applied to the detecting cathode is estimated, the sensor becomes explicit to the target gas. For electrochemical sensors of the small energy unit type,

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Fig. 2 The working principle of electrochemical sensors

an external driving voltage is not necessary. For instance, an oxygen-specific electrochemical sensor uses a Pb or Cd anode to supply electrons for cathode oxygen reduction [26–32]. Pros of electrochemical sensors • The range could be specific to a certain gas depending on the type and concentration of the intended to be detected. • Outstanding accuracy and repeatability. The sensor will consistently and accurately measure a target gas after the calibrated to a specific concentration. • Does not become contaminated by other gases. Other environmental vapors won’t reduce the sensor’s lifespan or make it shorter. Cons of electrochemical sensors • Life expectancy decreases with increasing exposure to the target gas. Typically, the maximum life expectancy of three years is mentioned. High temperatures and low humidity might dry out the electrolyte in the sensors. The electrolyte is also depleted by target gas or cross-sensitivity gas exposure. • A brief or restricted shelf life. • Other gases’ shared sensitivity can cause interference with some sensors. This has its benefits, but it can also have its drawbacks [28–35].

4 Optical Sensing Devices Light rays are transformed into electronic signals by an optical sensor [36]. It measures the actual amount of light and converts that measurement into a form that the instrument can read, much like a photo resistor [34–36]. The capacity to


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measure changes from one or more light beams is one of an optical sensor’s properties. Most frequently, this change is brought about by changes in the light’s intensity. The single-point approach or dispersion of points can both be used by optical sensors. A single-phase change is necessary for the sensor to be activated using the singlepoint approach. As far as the distribution notion is concerned, the sensor reacts along a broad array of sensors or a single fiber optic array [36, 37]. The Benefits of Optical Fiber Sensors over Traditional Sensors devices (TSD) now have a wider range of uses thanks to advancements in research and development, including in telecommunications and medical science [37]. Their productions were made to function with a wide range of physical characteristics. However, TSDs are more dependable and stiffer than conventional electrical and electronic sensors for performance in challenging conditions, where they struggle [36]. The benefits of Optical fiber sensors over other forms of sensors include the following [36–39]: • Are non-electrical devices that provide sensitivity to a variety of environmental factors and call for light cable weights and sizes. • Allow access to ordinarily inaccessible locations • Allow remote sensing, and frequently do not require contact. • Are immune to rust and do not contaminate their surroundings. • High sensitivity, resolution, and dynamic range are provided. • Data transfer systems can be interfaced. The operational principle of an optical sensor is based on the transmission and reception of light; the item to be detected interrupts or reflects a beam of light from the emitting diode. The resulting reflection of the beam is evaluated based on the equipment used. This enables the detection of things irrespective of the material used by the manufacturer [36, 37]. Many kinds of optical sensors exist today. Figure 3 as adapted from [34], describes the most common configurations of an optical sensor. In a through-beam sensor, the transmitter and receiver (which are situated across from one another), make up the system’s two individual parts. A beam of light is

Fig. 3 Optical sensors configurations

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directed toward the receiver by the transmitter. When the light beam is interrupted, the receiver interprets it as a switch signal [37]. For the Retro-Reflective Sensors configuration, the transmitter and the receiver are located in the same compartment. However, in Diffuse Reflection Sensors, one compartment contains both the transmitter and the receiver, and, the transmitted light is reflected by the intended target object [36, 37, 40].

4.1 Optical Sensing Applications Research on optical-materials sensing is ongoing worldwide, and these sensors are finding more and more uses in environmental monitoring, medicine, biomedicine, and chemical analysis. Although absorption and fluorescence are the primary physical phenomena utilized for optical chemical sensing, chemical luminescence as well as Raman scattering, and Plasmon resonance have also been reported [36, 40, 41], Undoubtedly, the application area that appears to have the most room for growth is healthcare. For several reasons, optical biosensors are finding more and more uses in various fields of medicine [36]. Optical sensing can help with several difficulties associated with monitoring electrical power generation, production, distribution, and conversion systems. Whether a hydroelectric turbine needs a special resistant system or a windmill needs a lightweight solution, optical sensing offers special features that precisely match with these formerly challenging applications [40, 41].

5 Piezoelectric Sensors By definition, piezoelectricity refers to a material’s capacity to produce electrical charge as a result of mechanical deformation [42]. The term “piezein,” which means to “squeeze” or “press,” is where the name originates from. The brothers Pierre and Jacques Curie first identified it in 1880 when they showed that different crystals, including zincblende, tourmaline, cane sugar, topaz, and quartz, exhibit piezoelectricity [42, 43]. After a few decades, the first real-world uses emerged. Using a quartz-based piezoelectric transducer, Langevin created an ultrasonic submarine detecting method in 1918. After that, during both World Wars, this strategy—known as sonar—was employed. The field of frequency control was introduced in the 1920s when quartz was used to stabilize oscillators, which is also widely acknowledged [43–45]. The electrical dipole serves as the foundation for piezoelectricity’s fundamental theory. A piezoelectric substance often has an ionic bonded crystal structure at the molecular level. Due to the symmetry of the crystal structure, the positive and negative ion dipoles cancel each other out while the system is at rest, hence an electric field cannot be seen. The crystal deforms under stress, loses its symmetry, and develops a net dipole moment [44]. Over the crystal, an electric field is created by this dipole moment. The direct piezoelectric effect, which causes electricity to


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be generated when stress is applied, is unique in that it is reversible, meaning that materials that exhibit it also do so in reverse, causing stress to be generated when an electric field is applied. The direct piezoelectric effect, which causes a material to produce electricity when stress is applied, is one of the special features of the piezoelectric effect. The material can also produce the opposite effect [44, 45]. In order to ensure that the directed pressure selectively loads the elements in a specified direction, pressure sensors are constructed with a thin membrane and a large base. The crystal components of accelerometers have a seismic mass associated with them. The way forces are applied to the sensing elements is the primary distinction between these two examples’ functioning principles [44]. While a connected seismic mass applies the forces in accelerometers, a thin membrane is employed in pressure sensors to transfer force to the environment. It is common for sensors to be sensitive to multiple physical parameters. When subjected to vibrations, pressure sensors provide erroneous readings. Therefore, advanced pressure sensors use acceleration correction components in addition to pressure sensing components. The correct pressure information is obtained by carefully matching those elements and subtracting the acceleration signal (released by the compensation element) from the combined pressure and acceleration signal. Vibration sensors can also be used to recover energy from mechanical vibrations that would otherwise be lost. To achieve this, mechanical strain is converted into useful electrical energy utilizing piezoelectric materials [43, 45, 46].

5.1 Working of Piezoelectric Sensor The basic principles of a piezoelectric sensor are as follows: • Charges in a piezoelectric crystal are perfectly balanced, even when arranged in an asymmetrical manner. • Because the effects of the charges cancel each other out, the crystal faces won’t have any net charge. • The crystal’s charge falls out of equilibrium as it is pressed. • As a result, from this point on, the effects of charge do not cancel one another, causing net positive and negative charges to emerge on the crystal’s opposing faces. • As a result, when the crystal is squeezed, voltage is generated over the opposing face; a phenomenon that is termed as piezoelectricity [44, 45]. In automotive applications, sound creation and amplification, liquid and fluid level measurement, and ultrasonic applications, piezoelectric sensors with a disc form are frequently used [43]. To detect changes in vibration or pressure and produce a usable electrical output, rings of piezoelectric sensors are used. Piezo ring sensors are frequently used in ultrasonic equipment for welding, cleaning, and dental purposes. Piezoelectric cylinders are another name for tube-shaped piezoelectric sensors. Piezo tube sensors are frequently used in the level, flow, and fiber optic sensors in sonar,

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mechanical, automotive, and scientific applications [44]. For vibration and pressure sensors, piezoelectric sensors with a plate or block shape are frequently utilized. Plate and block piezo sensors are frequently used in accelerometers and ultrasonic applications in a variety of sectors, including aerospace, automotive, and medical [45, 46].

6 Magnetic Field Sensing Devices Nowadays, magnetic sensors based on NMs are explored as promising sorbents in sample preparation techniques, such as food samples and the extraction of food components as well as the determination of pollutants levels in industries [19], due to their main advantages of; (i) reduced size (ii) ease of operation (iii) maintenance free and (iv) protection of contacts from oxidation, dust and corrosion owing to the glass bulb (hermetic) and inert gas [19] The various contacts are activated via magnetic field rather than mechanical parts. Magnetic devices are developed into Hall Effect (HE), Tunnel Magnetoresistance (TMR), Giant Magnetoresistance (GMR), Electromagnetic induction, Giant Magnetoimpedance (GMI) and Anisotropic Magnetoresistance, based on their physical phenomena [47]. The utilization of magnetic sensors with corresponding NMs manufacturing techniques makes it practical to integrate computing circuitry and sensing capability simultaneously [1, 2]. This makes the resultant chip-like systems very smart for internet applications. Additionally, the magnetoresistance and Hall sensors comprise ninety-eight of the magnetic sensor markets [7]. In the environment, various flexible magnetic sensors have been developed for healthcare and diagnostic purposes by applying novel approaches to investigating organisms, cells and chemical phenomena [48]. HE as a form of the magnetic sensor is a transducer determining magnetic fields that are built on the principle of the Hall Effect. It is the direct outcome of the magnetic Lorentz force (MLF), which deflects a moving charge carrier in a magnetic field. The MLF deflects the incident current when a field (magnetic) is applied perpendicularly to the current flow. As a result, opposite charges accumulate at the surface of the anode orthogonal to the flow of current, causing a Hall voltage at the equilibrium point [19]. The carrier mobility of the semiconducting MNMs is the leading factor determining the sensitivity of HE-sensors. Recently, silicon based HE-sensors with the robust and efficient monolithic fabrication of sensing elements are ubiquitous [49]. HE-sensor comes with some advantages [19]: • • • • • •

uncomplicated device architecture, low cost; ease in construction ease of integration with other circuits and scaling down; linear response; excellent robustness.


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However, the sensor, like other NM-based sensors [50], also suffers a number of shortcomings. HE-sensors usually have weak output signals when compared with other sensors, like magnetoresistive sensors. Additionally, finite offset signals and drifting with temperature in HE-sensors are major problems [19]. A good number of commercially available HE-sensors have an architecture with sophisticated electronics to overcome these problems [19] and amplify their output voltage. HE-sensors have been widely applied in devices such as power supply protection, flow-meters, pressure diaphragms, damper controls, rotary encoders, ferrous-metal detectors, tachometers, vibration sensors, etc. [49]. Typically, HE-sensors are generally rigid and thick, therefore limiting their applicability in the field of flexible and wearable electronics [19].

7 Conclusion Gas detection sensors will continue to be built on the foundation of MNM-based sensors since they are based on dependable technology. Robust and small MNMsensors have always been useful for personal and industrial gas detection and monitoring systems due to their dexterity. Electrochemical and optical sensing devices are still in their early stages of development, and new applications are being developed quickly. A significant portion of research continues to focus on the blending and joining of certain materials, both organic and nanoscale. This is likely to continue since the development of sensors with greater precision and sensors capable of making synchronous decisions has been a long-standing focus of research on sensors with the ability to operate in complex systems.

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Application of Magnetic Nanomaterials as Drug and Gene Delivery Agent Robert Birundu Onyancha, Bill C. Oyomo, Uyiosa Osagie Aigbe, and Kingsley Eghonghon Ukhurebor

Abstract Magnetic nanomaterials are characteristically biocompatible and superparamagnetic thus promising as drug carriers. They guarantee a controlled release of therapeutic materials to targeted sites, guard drugs from metabolization and mitigate their potential toxicity/side effects to healthy cells. Equally, they synergically work with thermotherapy and imaging (magnetic resonance imaging, near infrared optical imaging and magnetic particle imaging) through both local (hydrolysis, pH, conjugation of biomarkers etc.) and external (external magnetic fields, ultrasound, light etc.) stimulus in advancing medical treatment and therapy. Therefore, these materials are extremely important in biomedical applications, more especially in drug delivery systems. Based on the aforementioned, this chapter offers a brief introduction to magnetic materials, their synthesis and surface modification, stimuliresponsive control of drug release and a conclusion based on the reviewed research work. Keywords Magnetic nanomaterials · Drug delivery · Targeted sites · Local stimulus · External stimulus

R. B. Onyancha (B) · B. C. Oyomo Department of Technical and Applied Physics, School of Physics and Earth Sciences Technology, Technical University of Kenya, Nairobi, Kenya e-mail: [email protected] U. O. Aigbe Department of Mathematics and Physics, Faculty of Applied Sciences, Cape Peninsula University of Technology, Cape Town, South Africa K. E. Ukhurebor Department of Physics, Faculty of Science, Edo State University, Uzairue, Edo State, Nigeria © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 U. O. Aigbe et al. (eds.), Magnetic Nanomaterials, Engineering Materials,



R. B. Onyancha et al.

1 Introduction Nanomaterials (NMs) and their formulations have exclusively been explored by researchers and scientists in novel and varied applications (solar cells, catalysis, biomedical, material filters water treatment, etc.) owing to their physiochemical properties [1, 2]. Particularly, magnetic NMs have drawn unrivalled research interest due to their exciting properties which include small area, superparamagnetism, simplistic functionalization and large surface area. These properties have been exploited in the fabrications of magnetic inks [3], catalysis systems [4], magnetic fluids [5], gyroscopic machinery [6] environmental remediation [7] and biomedical fields [8]. In biomedical applications, magnetic NMs have been used extensively as therapeutic agents (drug delivery carriers) [9], magnetic separation [10], photo-hyperthermia [11], tissue engineering [12], biosensing [13] and in transfection of numerous vectors (both viral and non-viral) and magneto-infection [14] thus transforming medicine and pharmacology greatly. Therapeutic/drug delivery using magnetic NMs as nano-carriers/nano-vehicles has momentously gained interest over years. Importantly, drug delivery involves the release of conjugated therapeutic agents either encapsulated, physisorbed or grafted/ bounded onto NMs. The application provides an efficient and improved therapeutic effect of drugs by maximizing on biological and (super)magnetic properties of these materials. Drug release occurs in two main routes namely; (1) locally activated and (2) externally activated. Locally activated occurs through chemical or biochemical stimuli such as hydrolysis, pH, enzymatic activities etc. Conversely, externally activated requires the use of external stimuli such as light, ultrasound, external magnetic fields etc. [15]. The use of magnetic NMs over traditional administration as gene and drug delivery systems are many. For instance, they offer the possibility of use in procedures coupled with diagnosis and treatment of diseases which otherwise is unattainable in traditional administration. For example, controlled drug delivery can be used in tandem with hyperthermia. During magnetic hyperthermia, cancerous cells can be destroyed due to the low tolerance of elevated temperatures (42–49 °C) [16] and thermal stimulus can ensure the release of loaded drugs to the targeted site thus synergically providing efficient treatment procedures [17]. Equally, a combination of drug systems with imaging capabilities like MRI, MPI and NIR provides excellent theranostics (combination of therapy and imaging) [18]. This is made possible due to their many characteristics (pharmacokinetics, drug release, solubility of drug, penetration and retention, biodistribution and cytotoxicity) which are advantageous over conventional methods (Fig. 1). It is worth-noting that conventional/traditional drug administration is ordinarily administered through parental, oral, transdermal or pulmonary routes thus demands for many doses for optimum efficiency. Nevertheless, the use of nanomaterials as control drug release agents ensures a reduction in the quantity of drug administered, minimizes toxicity and maximizes the available dosage thus overcoming the shortcomings of conventional routes. In particular, this system is crucial in the treatment of

Application of Magnetic Nanomaterials as Drug and Gene Delivery Agent


Fig. 1 Advantages of Magnetic NMs as drug carriers over conventional methods/systems

diabetes or persons using anti-inflammatory medicines since insulin will be readily released on demand for the former and the availability of drug concentration in the blood stream guarantees no pain in the latter [8]. Until now, multiple magnetic NMs have been synthesized and are typically consisting of pure metals (Co, Ni and Fe), metal alloys (FePt, CoPt), ferrites, or metal oxides. Notably, iron-based oxide NMs have been the most explored. They include the Fe3 O4 -crystalline magnetite or γ − Fe2 O3 -maghemite. In the fabrication of nano-systems for drug delivery, their surface charge, intrinsic magnetic properties, size, toxicity and degree of stability in aqueous substance must be considered. Normally, small-sized NMs (